(CNN) -- Police arrested four people Monday in connection with a nightclub fire that killed 231 people in southern Brazil, CNN affiliate BandNews reported.
Two are club owners and the other two members of the band that was performing, it said.
The detainees will be held initially for five days while authorities investigate Sunday's blaze in the Kiss nightclub in Santa Maria, according to Marcos Viana, a police official who spoke with 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.
The police chief in the province of Rio Grande do Sul said the investigation is to be divided into three parts: "The first line of inquiry has to do with the documentation: if the property was fit for operation and who the owners are. Are they real, formal owners? We will review all the documentation.
"The second stage of this investigation is expert analysis, which we will apply.
"And thirdly, important in itself, is the witness testimony. So, starting today, we will focus our efforts to the maximum in order to hear those people who were at the property at the time that it caught fire, at the business establishment. I think we'll get to the bottom of this investigation and, if possible, will identify those responsible by the time we complete this police investigation."
The governor of Rio Grande do Sul promised that investigators would have all the resources they need to find out who is responsible.
"From the executive office, they will not lack a penny, a document, an action or any other support, so that we can have an inquiry with depth and with the responsibility that it deserves," Gov. Tarso Genro said.
More than 100 clubgoers were injured in the fire, which authorities say began about 2:30 a.m. Sunday during a band's pyrotechnic show.
Guitarist Rodrigo Lemos Martins of the Gurizada Fandangueira band told the newspaper Folha de São Paulo that the fire ignited one song after the band had used fireworks in the show. But he said it was not clear what may have caused the fire.
"There were many wires on the ceiling, and there could have been a short circuit," he said.
Many apparently died from smoke inhalation; others were trampled in the rush for the exits.
Mayara Peirera, a 21-year-old law student who was celebrating her birthday at the club, told CNN she escaped with a friend through a nearby door. When she turned to look back, "I saw people bleeding, fainting, running over other people. People desperate, screaming. And it was then I realized what was going on," Peirera said.
But two friends -- "almost sisters to me" -- didn't make it out, she said.
"I thank God because in one way or another, I got a birthday gift -- my life," she said. "I was born again, but I'm very sad and hurt because I lost my best friends. I can no longer cry, because I have already cried so much."
And Michele Pereira told Folha de São Paulo that her friend, 23-year-old Leandra Toniolo, was in the bathroom when the fire began.
"I was on the opposite side, near the stage," Pereira said. "I would have had to go all the way across the arena -- against the mayhem -- to find her, and in the tumult, it was impossible," she said. "It was terrible, a scene from a horror film. ... There were fallen bodies throughout on the ground, many people who had fainted, many crying and trying to breathe with all that smoke."
By the time Toniolo's mother found her daughter's body, it had been placed with others in a truck, Pereira said.
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 been held at the city's municipal cemetery, its chief of staff told 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.
CNN's Tom Watkins, Helena Cavendish deMoura, Shasta Darlington and Chelsea J. Carter contributed to this report.