Footage of the beginning of the blaze
Russian President Dmitry Medvedev has declared a national day of mourning on 7 December after a fire at a nightclub killed at least 109 people.
He said the fire was a criminal act and those responsible must be punished.
Officials say fireworks inside the club caused Friday's blaze and that most victims died from smoke inhalation.
More than 140 people were reported injured at the Lame Horse club in Perm, some 1,400km (870 miles) east of the capital Moscow.
Speaking on Saturday, Mr Medvedev said those responsible "have neither brains, nor conscience", calling for the toughest possible punishment.
RECENT RUSSIAN FIRES
June 2007 - 10 people die at retirement home in Siberia
March 07 - 63 people die at old people's home in southern Krasnodar region
March 07 - 10 people die at Moscow's 911 nightclub
Dec 06 - 45 women die at Moscow's drug clinic
Dec 05 - seven people die at home for mentally ill near Moscow
Russian officials said earlier they had arrested the owner of the nightclub and other suspects, following the accident on Friday night.
They said the nightclub had ignored repeated warnings about its fire safety.
Such complacency is endemic across Russia, the BBC's Rupert Wingfield-Hayes in Moscow says.
He says that locking fire escapes is routine even in Moscow office buildings and is one reason Russia had 18,000 fire deaths last year.
The Lame Horse nightclub had been celebrating its eighth anniversary on Friday night.
Russian television has shown a video recorded by one of the guests at the celebrations.
The footage shows people dancing in the club before sparks from onstage fireworks ignite the building's ceiling.
Svetlana Kuvshinova, who was in the club when the fire began, said the flames "took seconds to spread".
"It was like a dry haystack. There was only one way out. They nearly stampeded me," the Associated Press quoted her as saying.
Another eyewitness told local TV: "When the merry-making started, when they were warming up, they set off fireworks.
"When I turned back, I saw drops falling off the ceiling and then there was a lot of smoke. Later this huge flame was moving along the ceiling," the unnamed woman said.
Regional public security minister Igor Orlov told Itar-Tass news agency: "People panicked and succumbed to burns, general crush and gas poisoning."
A spokesman for the prosecutor-general's main investigative unit told the news agency that it was not a terrorist attack.
The Russian government has set up a special commission to deal with the incident.
Regional officials said that fireworks used at the party were too powerful for enclosed premises and were intended for outdoor use.
Perm has a population of 1.2 million and is the sixth largest city in Russia.
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