BAGHDAD, Iraq (CNN) -- More than one million Iraqis have been forced from their homes by conflict this year, the U.N. refugee agency said Friday -- a number only likely to rise as Islamist militants and Iraqi Security forces battle for control.
A humanitarian crisis is brewing, as families who've fled fighting with little more than the clothes on their back seek water, food and shelter from the summer heat.
Meanwhile, the first of up to 300 U.S. military advisers will arrive in Iraq as soon as Saturday, a senior defense official told CNN. This first group from outside Iraq is expected to be very small, the official said.
In addition, some U.S. military personnel already in Iraq at the security cooperation office in the U.S. Embassy in Baghdad will be reassigned and become the first of the advisers to go to work, Pentagon press secretary Rear Adm. John Kirby said.
Concern for the soaring number of people displaced in Iraq comes as the Office of the United Nations High Commissioner for Refugees (UNHCR) marks World Refugee Day on Friday. Its report, based on data up to the end of 2013, finds that the number of refugees, asylum-seekers and internally displaced people worldwide has, for the first time since World War II, exceeded 50 million people.
Now the crisis in Iraq -- which was already sheltering hundreds of thousands displaced by the war in Syria -- is swelling that number even more.
An estimated 500,000 people fled Iraq's second-largest city, Mosul, last week after it fell to fighters from the Islamic State in Syria and Iraq. On Friday, the International Committee of the Red Cross in Iraq put the number who fled Mosul, with its population of 1.6 million, at about 800,000.
Already, a half million peop,e were displaced from Iraq's western Anbar province, where Sunni militants have been dominant since early this year.
Added to that are tens of thousands more who have fled their homes in Diyala and Salaheddin governorates amid the recent violence, UNHCR spokeswoman Ariane Rummery told CNN.
Will the number soar still higher? "In terms of the number of displaced people, that really depends on what happens," Rummery said. "But what we know is that conflict and violence fuel displacement.
"With the humanitarian situation, we know that there's a million people displaced and it's not always easy to get to all of them."
While some fleeing families have taken rooms in overcrowded hotels, others, low on funds, have had to take shelter in transit camps that have sprung up near checkpoints controlling entry to Iraq's Kurdish-controlled north.
Those who have fled to the Kurdish region are easier to reach, Rummery said, but others have sought safety in less accessible regions.
U.N. High Commissioner for Refugees Antonio Guterres, speaking in Beirut, warned that any mass exodus of refugees from Iraq could be hard to cope with, given the regional situation. "I hope that this outflow will never come because the capacity of the region to deal with it is practically nonexistent," he said.
Jacqueline Badcock, U.N. humanitarian coordinator for Iraq, said agencies were moving fast to try to meet the needs of Iraq's newly displaced population, despite the volatile situation.
"Food, water, tents and other essential supplies are reaching families in need, additional staff are being mobilized, and emergency funds are being released," she said. "I remind all parties to the conflict that they must allow unfettered and sustained humanitarian access to all people in need."
U.S. sending military advisers
For days, the United States has considered what to do about the militants, and on Thursday, President Barack Obama said he was prepared to send as many as 300 military advisers to Iraq, adding that America was not returning to a combat role in the country.
The Pentagon earlier presented Obama with a plan to send up to 100 special forces advisers to Iraq to work along with that country's military, several U.S. officials told CNN on Thursday.
The first group of advisers will begin work by conducting an initial assessment of Iraqi troop capabilities and on what may be needed for a larger group of U.S. advisers, including additional security measures where they may be deployed, a senior defense official said Friday.
But the United States has not reached an agreement with Iraq to provide legal protections to the U.S. military advisers.
"We are pursuing something in writing," Kirby said Friday. He said Defense Secretary Chuck Hagel "is absolutely committed to making sure that our troops have the legal protections, and he would not do that on a nod and a wink."
Kirby said the U.S. did not foresee a problem getting the Iraqi government to sign such an agreement because Iraq had requested this U.S. support.
The Pentagon has identified two preliminary locations in Baghdad and northern Iraq for proposed joint Iraq-U.S. operations centers, but those locations are not being disclosed at this point because of security concerns, the official said.
The United States withdrew its final troops from Iraq at the end of 2011, nearly nine years after leading the invasion that ousted longtime leader Saddam Hussein.
Putin backs government
As ISIS, born from an al Qaeda splinter group and supported by many Sunni factions, continues its fierce advance in Iraq, senior U.S. officials tell CNN that the Obama administration is of the belief that Prime Minister Nuri al-Maliki is not the leader Iraq needs to unify the country and end sectarian tensions.
The Prime Minister's Shiite-dominated government is accused of fostering sectarian tensions by marginalizing Iraq's Sunni Arab and Kurd minorities.
The officials, along with Arab diplomats, say the White House is now focused on a political transition that would move Iraqis toward a more inclusive government -- one without al-Maliki that would include Sunni, Shiite and Kurdish factions.
Russia, however, expressed its support to the Iraqi government when al-Maliki received a phone call from President Vladimir Putin, the media center for the Iraqi government said Friday.
The leaders discussed the situation in Iraq, and Putin backed the Iraqi government's fight against terrorist groups, according to the Iraqi government.
U.S. Secretary of State John Kerry will begin several days of travel Sunday to Jordan, Belgium and Paris to talk about how allies can support Iraqi stability and an inclusive Iraqi government and to attend the NATO Foreign Ministerial.
In Iran, thousands of worshippers roared their approval as Tehran's powerful Friday prayer leader condemned ISIS but stopped short of calling for fighting forces and volunteers to be deployed inside Iraq.
The prayer leader also blamed western powers for the violent insurgencies that are plaguing the region.
Top cleric urges all Iraqis to unite against ISIS
Al-Maliki has called for Iraqis to join the military's fight against the Sunni extremists -- a call echoed a week ago in a message from Ayatollah Ali Sistani, the most powerful Shiite cleric in Iraq.
But a senior religious Shia cleric clarified Friday that the top Iraqi Shiite leader was calling for all sects to stand together against ISIS, and not for the country's Shiites to take up arms in a new militia force.
The government should ban all militias and armed groups other than Iraq's security forces, Imam Sayid Ahmed Al-Safi said at Friday prayers in Karbala.
Additionally, he said Iraqis should respect the timeline set by the high court to name the new presidential Cabinet and ministerial positions, following recent elections. Al-Maliki's party came out on top in the balloting, but many in Iraq do not want to see him continue as Prime Minister.
Al-Safi also urged Iraqis not to engage in price gouging. The cost of essentials such as food and cooking gas has soared in recent days, adding to people's anger.
Iraq's military is also calling for retired aircraft technicians, mechanics and officers to re-enroll for active service, the Ministry of Defense announced Friday. They will get their old titles and salaries back.
Meanwhile, what purported to be a slick, English-language propaganda and recruitment video for ISIS was posted to YouTube on Thursday, appealing for Western jihadists to join the militant group. CNN cannot independently confirm the authenticity of the video.
Precious seats on flights
The ISIS fighters, who have vowed to take the capital, have come within 40 miles (64 kilometers) of Baghdad with their assault on the town of Baquba.
The sense of fear was palpable Thursday at Baghdad International Airport, where hundreds of people waited in long security and check-in lines for one of the few, precious seats available on flights out of the capital.
Many people are seeking safety in Iraq's Kurdish-controlled north, particularly Irbil, or in the southern port city of Basra. Others are trying to leave the country altogether.
To accommodate the exodus, airlines have begun adding flights and, in some cases, much larger planes. Still, there are few seats available as most flights, according to travel agencies, are sold out weeks in advance.
Where once there was one Iraqi Airways flight a day to the northern city of Irbil, there are now three.
Amid growing unease, Australia's Defense Department said a small military contingent had been deployed to help protect the Australian Embassy in Baghdad.
Iraq reclaims refinery
Iraqi security forces regained control of the Baiji oil refinery, the largest in Iraq, on Friday following a night of fighting, Iraqi security officials in Samarra told CNN.
Iraqiya State TV reported that Iraqi security forces killed an undisclosed number of ISIS fighters.
Clashes erupted, however, elsewhere near Bajii on Friday, security officials in Samarra told CNN. At least 12 militants were killed.
Iraqi air forces also conducted strikes on areas near Baiji on Friday. Baiji is predominantly Sunni town about 200 kilometers north of Baghdad.
In the northwest, dozens of militants believed to be ISIS attacked the Tal Afar air base about 70 km west of Mosul on Friday, said police in Baghdad and Samarra.
Iraqi security forces foiled the attack and killed at least 15 militants, police said.
Attackers then withdrew from the air base and went back to the city. The air base is still under control of the Iraqi security forces, but a large part of Tal Afar town is still under the ISIS control, police said.
ISIS attackers have been trying to take over the Tal Afar airbase since last week. Tal Afar is used to be mixed town of Sunni and Shiite Turkmen, but during the sectarian violence in 2005, 2006 and 2007, most Sunnis fled.
Since then Tal Afar has become a town of largely Shiite Turkmen. But last week, when ISIS attacked the town, thousands of Shiite Turkmen families fled to the Kurdish region.
In al-Qaim along the Syrian border, Iraqi security forces back by Sunni tribes killed at least 17 ISIS fighters and destroyed nine of their vehicles in clashes at dawn Friday, said Iraq's media center, citing security officials.
Iraqi security forces were still pursuing the militants Friday, the government said.
In the north, two Kurdish Peshmerga were killed and three others were wounded when suspected ISIS fighters attacked a Kurdish military post about 70 kilometers southeast of Kirkuk on Friday, said Kurdish security forces in Kirkuk.
Kurdish forces started shelling nearby areas, officials said.
In the town of Al-Azzi, militants believed to be ISIS fighters attacked a security post, wounding soldiers and police.
And in Diyala province near Muqdadiya, Shiite militiamen joined security forces in fighting off attacks on predominantly Shiite areas. The militiamen had recently taken over security in some parts of Muqdadiya, according to police in nearby Baquba and Baghdad. The government recently opened a recruiting station in Muqdadiya for volunteers to join the military to fight ISIS.
ISIS takes old chemical facility
Also on Thursday, ISIS militants took control of a facility that Saddam Hussein once used to produce and store chemical weapons.
But the State Department doubts that the Al Muthanna complex contains any material of "military value."
"The materials in the bunkers, which date from the 1980s, are of little military value and would be very difficult to safely move," State Department spokeswoman Jen Psaki said Thursday. But "the materials pose serious health hazards to anyone attempting to access the bunkers."
Pentagon spokesman Kirby said whatever material was kept there was "pretty old and not likely to be able to be accessed or used against anyone right now."
Kirby added that the information the United States has is imperfect and that any progress ISIS has made is of concern.
He added that the United States does not view this particular site as a major issue at this point. He said that even if the militants could access the chemical weapons material, it is more of a threat to the militants than to anyone else.
CNN's Chelsea J. Carter reported from Iraq and Laura Smith-Spark reported and wrote in London. CNN's Nic Robertson in Baghdad, Mohammed Tawfeeq, Khushbu Shah, John Raedler, Sherko Raof and Michael Martinez contributed to this report. Reza Sayah contributed from Tehran.