At least 109 people have been killed and 140 others injured in a blast caused by fireworks at a nightclub in Perm, a Russian city located near the Ural mountains.
The explosion occurred in the Lame Horse bar in the centre of the city, where over 200 people were partying early on Saturday, Russia's Itar-Tass news agency quoted a local police official as saying.
A regional emergency situations ministry spokesman said earlier that 102 people had died, but officials and witnesses later revised the toll to 109.
Law enforcement officials ruled out the possibility that the blast was a "terrorist" act.
National mourning
Dmitry Medvedev, the Russian president, ordered a national day of mourning for December 7 and demanded tough action against owners of the nightclub.
He said they had repeatedly ignored warnings from fire inspectors that the premises were unsafe.
"They have neither brains nor conscience," Medvedev told ministers in a televised meeting, scolding the club's owners for failing to come forward immediately after the disaster.
Vladimir Markin, a senior judicial official, was quoted by Interfax as saying: "The accident was due to a violation of instructions when launching fireworks."
Itar-Tass news agency quoted a spokesman for the prosecutor-general's main investigative unit as saying: "We are not talking about a terrorist attack, we are talking about a failure to observe fire regulations."
Al Jazeera's Neave Barker, reporting from Moscow, said: "Details are sketchy at the moment but several different Russian news agencies are all reporting that up to 94 people may have been killed while several others are saying that over 100 people may have been killed in total in the incident."
Dozens of clubbers who sustained burns are in critical condition and have been sent to Moscow for specialist help, our correspondent said.
"Medical teams and equipment have been flown into Perm to help the medical staff there - clearly overstretched by an incident of this magnitude," he said.
"An investigation has now begun and, according to local sources, the manager and owner of the club have been detained pending an inquiry.
"Officials have been cited as saying that the incident may have been caused by pyrotechnics that caused an explosion leading to a significant loss of life."
Carbon poisoning
A police source told RIA Novosti that most victims succumbed to carbon monoxide poisoning as the panicked crowd rushed to escape.
Russian state-run television channel Vesti-24 showed charred bodies piled on top of each other in the snow-covered street outside the club, where firemen and investigators cleared debris and recovered bodies.
The blast follows a deadly train bombing last week, which killed 26 and injured over 100 on a luxury train travelling between Moscow and St Petersburg, for which Chechen armed groups claimed responsibility.
Perm, the sixth largest city in Russia, has a population of 1.2 million people.