An entire section of a nine-story apartment building in the city of Astrakhan collapsed Monday after a gas explosion on a lower floor, killing at least six people, Interfax reported.
Rescuers reported that 18 people were injured in the accident and that six had been killed as of Tuesday morning. Four people thought to have been inside the building when it collapsed remained unaccounted for.
Regional investigators said Monday afternoon that the explosion took place in a store on the first floor of the building, but later they said it likely occurred on the third floor. There was construction work under way on the entrance to the building.
A witness told the news agency that the bottom floors were destroyed initially, followed by those above, causing rescuers to be trapped in the rubble.
"First there was an explosion, approximately in the area of the second or third floor, and the second and third floors collapsed — the wall came down. I saw two people scramble out of there. We crawled in to help, and at that moment the other floors collapsed. I saw two people get buried, and another few who went in there remained inside," the unnamed witness said.
Investigators said the explosion was likely the result of a suicide attempt by a man living on the third floor who had threatened to kill himself on multiple occasions in the past.
"In one apartment [on the third floor], there was a man who periodically brought up thoughts of suicide. He turned on the gas [oven] burners on multiple occasions. And, it seems, before the explosion he carried out this action," Astrakhan Investigative Committee head Sergei Bobrov said, RIA-Novosti reported.
Bobrov said the possibility of a terrorist attack having been the cause of the explosion could not be ruled out, but that it was highly unlikely, given the absence of evidence that an explosive device had been detonated.