(CNN) -- Police arrested three people and were searching Monday for a fourth in connection with the nightclub fire that killed 231 people in southern Brazil, state media reported.
The detainees will be held initially for five days while authorities investigate Sunday's blaze in the Kiss nightclub in Santa Maria, Marcos Viana, a police official told state-run Agencia Brasil. The five-day period can be extended for five more days, the news agency said.
"We concluded that it was necessary to hold them prisoner temporarily, because we need their statements to help us clarify the incident," Viana said, according to Agencia Brasil.
Police did not identify those arrested.
"We have much work ahead to clarify what happened and identify those responsible," Viana said, according to the news agency.
Civil police in Santa Maria have questioned 20 other people, it said.
More than 100 clubgoers were injured in the fire, which authorities say began about 2:30 a.m. Sunday when a band's pyrotechnic show ignited insulation material.
Many apparently died from smoke inhalation; others were trampled in the rush for the exits.
The nightclub owners have pledged to cooperate with the investigation, according to a statement released by the law firm of Kummel & Kummel.
"We are open to all authorities and inspections," said the statement, obtained by Globo TV.
The club's license had expired in August and had not been renewed, a local fire official told Globo TV.
The owners, however, said the nightclub was properly permitted and had been inspected by the fire marshal.
The city's mayor, Cezar Schirmer, said the fire department "has always done a very strict surveillance on the homes of shows and dealt with all other issues that relate to security of these places."
On Monday, the first of Brazil's three days of mourning, flowers were left outside the club in tribute to the victims, and a flag outside the country's presidential palace flew at half-staff.
In Santa Maria, mourners lined up in a series of funeral processions and coffins were lined up in a gymnasium that authorities had turned into a morgue.
By noon, 40 of 110 funerals planned for the day had already been held at the city's municipal cemetery, its chief of staff told CNN affiliate Band News.
At one funeral, air force troops fired rifles in tribute to a comrade who died in Sunday's fire.
At another, two teenage brothers, the only children in one family, were buried side by side.
Of the people who were hurt, 82 were still in area hospitals; 40 were taken four hours east to the city Porto Alegre, BandNews TV reported.
The governor of Rio de Janeiro sent 15 mechanical ventilators, Agencia Brasil reported.
By Catherine E. Shoichet and Umaro Djau
CNN's Tom Watkins, Shasta Darlington and Chelsea J. Carter contributed to this report.