A powerful explosion ripped apart a nine-story apartment building on the southeast fringes of the capital Thursday, killing at least 32 people, injuring more than 150 and burying more than 50 under the smoldering rubble. Emergency workers held out little hope of finding more survivors.
"It's like hell underneath," one rescuer said. "Even if they survived the blast they would have been burned."
By Thursday evening, investigators were still trying to determine the cause of the overnight blast at 19 Ulitsa Guryanova, which experts said was equal to up to 400 kilograms of TNT.
Investigators said early Thursday that a natural-gas explosion was one possibility, but as the day wore on they determined that a bomb was more likely. Yet another theory suggested that explosives stored in the building went off accidentally.
"The nature of the damage and the number of casualties'' suggests an explosive device was placed in the building, the Federal Security Service said in a statement. The FSB said no one had claimed responsibility.
Moscow Mayor Yury Luzhkov called it a terrorist act and blamed Islamic terrorists. "They could be trying to take revenge for their first defeat in Dagestan," Luzhkov said at the scene.
Vladimir Minayev, head of the Prosecutor General's Office's main investigative department, said they are looking into a possible connection to the deadly explosion last weekend at a army compound in the Dagestani city Bunaiksk, which killed more than 60 people.
"We cannot rule out a possible link to the events in the North Caucasus," Minayev said at the scene. A joint team from the prosecutor's office, the FSB and the police had been set up to lead the investigation, he said.
It was the second mysterious explosion in Moscow in a little over a week, following the Aug. 31 blast at the Manezh shopping center in the heart of town.
The explosion Thursday was in a much more obscure location, but Luzhkov said "an explosion in any point in Moscow will always be the subject of extreme media attention."
Moscow police were put on high alert, he said at an afternoon news conference, "but there are no measures that could guarantee total protection."
Although Russia has been shaken in recent days by the terrorist attacks, past explosion also have been caused by poor maintenance and shoddy construction. A gas blast in a Moscow apartment building in July 1998 killed six people.
Vladimir Stavitsky, the FSB's deputy press chief, said that either industrial explosives equivalent to 300-400 kilograms of TNT or a great quantity of explosives used in fireworks had caused Thursday's blast, The Associated Press reported.
The FSB has identified possible suspects and begun to search for them, he said.
Sergei Bogdanov, spokesman of the FSB's Moscow branch, said that the blast may have been caused by explosives stored in the building.
"It's common knowledge that there are warehouses of the most incredible things in basements and rented apartments,'' he told NTV television.
Igor Matrosov, whose apartment is in one of the entrances less damaged by the blast, said there were several stores on the ground floor, including one that sold chemicals and paints. He said none of the entrances' doors had locks and the basement could have been accessed by anyone capable of breaking its simple padlocks.
Luzhkov, who has a degree in chemistry, said that for a gas explosion the amount of propane needed to cause such destruction would be immense. He also added that gas explosions usually are followed by large fires, which was not the case Thursday.
He announcing later Thursday that a military explosive called hexogen was the most probable cause of the blast, Interfax reported.
Hexogen, also called RDX, was used by most of the warring powers in World War II. A hard, white crystalline solid, its principle non-military use is in blasting caps.
The explosion shortly after midnight collapsed all nine stories in the center section of the block-long building, but left apartments intact on either side. The building is on the edge of one of the huge complexes of apartment buildings that ring Moscow, and is bordered on one side by grassy fields and railway tracks.
The explosion shattered windows in buildings hundreds of meters from the blast scene and turned over cars in surrounding streets.
Rescue teams used cranes, bulldozers and dump trucks to remove mangled trees and huge slabs of shattered concrete. The emergency workers were hampered by the thick smoke.
What looked like part of a human torso could be seen pressed between two massive pieces of concrete, but rescuers paid no attention, focusing instead on trying to save anyone who could still be alive.
All they pulled out, however, were charred bodies, as flames continued to pop up from the depths of the rubble 14 hours after the explosion,forcing rescuers to give way to firefighters.
All operations at the site were put on hold after several pieces of concrete fell from upper floors in what appeared to be a narrow escape for the rescuers.
As of 3 p.m., 152 persons were registered as injured, including 19 children, said Anatoly Nikitin, senior official with the medical service of the Emergency Situation Ministry's Moscow branch. Of that number, 73 people, including 17 children, had been hospitalized.
Emergency Situations Minister Sergei Shoigu said Thursday evening that about 50 residents of the building were still unaccounted for.
Luzhkov said that a total of 15 buildings were damaged - mainly shattered windows - and a nearby school and kindergarten lost windows, doors and door frames. About 800 apartments would have to be repaired, while the people registered in 286 apartments would have to be relocated. He said the necessary money would be cleared by Friday afternoon.
The mayor said it was still not clear whether building No. 19 could be rebuilt or would have to be torn down.
An anonymous caller told Interfax on Thursday that the apartment explosion and a Saturday night bomb blast in Buinaksk, Dagestan, were in response to Russia's military campaign against Islamic rebels in the southern territory of Dagestan.
Earlier this week, the Moscow correspondent of Deutsche Welle, Germany's international broadcasting service, received a call from a man warning there would be three explosions in Moscow. He said they were "an act of revenge for the bombing of Chechen villages by the Russian army,'' Deutsche Welle reported.
The claims' authenticity could not be confirmed.