The death toll in a New Year's Eve apartment-building collapse rose to 37 as rescuers working in frigid temperatures pulled bodies from the rubble in the Russian city of Magnitogorsk and speculation about the cause of the disaster swirled.
"The bodies of two more women and a man were recovered," a spokesperson for the Emergency Situations Ministry said on January 3 after the death toll was raised from 33.
The ministry said that four people remained unaccounted for more than 48 hours after an explosion sent part of a 10-story building crashing to the ground.
Six children were among those confirmed dead, the ministry said. Six people -- including an infant whose rescue has been called a miracle -- have been pulled alive from the rubble of the building in the southern Urals city and hospitalized.
Russian authorities have said since shortly after the December 31 collapse that a natural-gas explosion was the most likely cause.
But in a statement issued on January 1, the federal Investigative Committee said the authorities were looking into "all possible causes" and added that no signs of a bomb blast have been found.
"In connection with various reports that have appeared in the media, it must be noted that at the present moment...no traces of explosives or their components have been found," the statement said.
The committee issued the statement after two media outlets cited unnamed sources as saying that possible traces of explosives were found at the site and that the blast that caused the collapse could have been a terrorist act.
The reports in znak.com and regional news site 74.ru, which could not be independently verified, also linked the building collapse with an incident late on January 1 in which a van caught fire some 3 kilometers from the site, killing three people.
The site 74.ru cited unnamed law enforcement sources as saying that the occupants of the vehicle were suspects who were being sought by police, possibly in connection with the building blast and collapse.
The Federal Security Service (FSB) said that there were two gas canisters in the vehicle, and the regional Interior Ministry branch said that the fire may have been caused by a gas-canister explosion.
Speculation was stoked by Internet-posted footage of the burning van in which a series of loud bangs that sound like gunfire can be heard.
Several deadly apartment-building explosions in Russia in the past 25 years have been blamed on militants from the North Caucasus, the site of two wars between federal forces and Chechen separatists as well as an Islamist insurgency rooted in those conflicts.
But household-gas blasts have also been blamed for many such disasters, and when part of an apartment building collapses, there is frequently speculation about the cause.
Investigative Committee Director Aleksandr Bastrykin has set up an investigative group of some 100 officials to work on the case.
January 2 was an official day of mourning in Chelyabinsk Oblast, where Magnitogorsk -- an industrial city of some 400,000 people some 1,700 kilometers southeast of Moscow -- is located.
On January 1, an infant found by rescuers alive in the rubble some 35 hours after the explosion was flown to Moscow for medical treatment.
Russian officials said the infant was found lying in his crib wrapped in layers of blankets, which likely saved his life.
The child -- identified as Ivan Fokin -- suffered frostbite, broken bones, and a head injury.
His mother and father survived the explosion and subsequent collapse of their apartment. The father, Yevgeny, has called his son's rescue "a New Year's miracle."
Authorities had been forced to temporarily halt most of the rescue operations because of fears the efforts would dangerously shift rubble.
PHOTO GALLERY: Suspected Gas Explosion Devastates High-Rise In Russia's Magnitogorsk (CLICK TO VIEW)
"There is a real risk that more sections of the building will collapse," Russian Emergency Situations Minister Yevgeny Zinichev said on January 1.
Later, rescuers removed some dangerous segments of the building and resumed their operations.
Rescuers had braved temperatures as low as minus 17 degree Celsius through the night in an effort to locate victims.
Large heaters were brought in to try to keep any possible survivors from freezing to death as the rescue operations continue.
"We must work as quickly as we can since temperatures do not give us any time to linger," Deputy Emergency Situations Minister Pavel Baryshev told journalists.
President Vladimir Putin traveled to the site on December 31 and met with local officials before visiting some of the injured at a nearby hospital.
According to the regional government, the explosion took place at 6:10 a.m. local time on December 31 in a complex of apartment buildings that was built in 1973 and houses some 1,100 people.
The Emergency Situations Ministry said on its website that, in all, 48 apartments from the third to the 10th floor in the building's central part were damaged by the explosion.
Magnitogorsk, an industrial city of some 400,000 people, is located some 1,700 kilometers southeast of Moscow.