Moscow, Russia (CNN) -- Suspects in an explosive inferno at a Russian nightclub that killed at least 112 people will face charges Monday, authorities have said.
The fire broke out Friday night in the Ural Mountain area industrial city of Perm, sweeping through a party in full swing at the Lame Horse, a nightclub celebrating its eighth year in business. An estimated 300 people were in the club.
Authorities have cited five suspects. Three people are suspected of violating fire safety regulations, and the director of the company that supplied and installed fireworks equipment in the nightclub could face manslaughter charges, said Marina Zabbarova, head of the Perm territory branch of the Investigative Committee. Authorities detained those four suspects.
A court ruled Sunday that the four will remain under arrest for two months, according to local prosecutor Vladimir Rybailo.
Another suspect was hospitalized, in critical condition. "He is the owner of the Lame Horse premises," Zabbarova said.
More than 170 interrogations have been conducted with injured people and eyewitnesses, said Vladimir Markin, a spokesman for the Investigative Committee of the Russian Prosecutor's Office.
At least 123 people were hospitalized, authorities said.
The death toll climbed to 112 on Sunday, rising as people died in hospitals, according to the press office of the Perm division of the Russian Emergency Situation Ministry. Three victims were buried Sunday, Russian media reported.
As of Sunday morning, 26 people remained at area hospitals, with the rest airlifted to burn trauma clinics in Moscow, St. Petersburg, Chelyabinsk and Nizhni Novgorod, according to the Russian Emergency Situations Ministry.
Patients who were not transportable were being treated by medical teams that were sent to Perm with mobile hospitals.
Russia was to observe a national day of mourning Monday, according to presidential decree.
The four detained suspects were the co-owner, the executive director, and the art director of the nightclub, and a businessman who supplied and organized fireworks, said Vladimir Markin, a spokesman for the Investigative Committee of the Russian Prosecutor's Office.
Fireworks are suspected as the main cause of the blaze, but investigators are looking at other possibilities as well, including a possible short circuit, Zabbarova said. Toxic smoke killed most of the victims, she added.
"A lot of people were lying on the floor of the club," according to one young female witness. "Those of them who breathed were carried out and put in cars. The biggest problem was that each ambulance took only one person. They didn't take any more. We were yelling at doctors, forcing them to take more people at once."
On Sunday, people in search of missing loved ones were looking through page after page of victims' names.
Area residents placed flowers outside the burned club in memory of the victims, a scene that brought back memories of two other deadly club fires in Russia: one in Moscow in 2007, the other in Omsk in 2008.
The tragedy shocked Russians, reeling after last week's derailment of a luxury express train from Moscow to St. Petersburg.
That incident -- which killed 26 people and injured more than 100 others -- has been called a terror attack, the most lethal terrorist act outside of Russia's troubled North Caucasus region since 2004.
In a televised address from his country residence near Moscow, President Dmitry Medvedev demanded that those responsible for Friday's fire receive the harshest possible punishment.
He sent government officials to Perm to handle the aftermath of the fire, organize medical assistance to survivors and investigate. Prime Minister Vladimir Putin dispatched planes from Moscow equipped to carry people with extensive burns.
CNN's Max Tkachenko in Moscow contributed to this report