MOSCOW - A suicide bomber detonated explosives at the entrance to a railway station in Volgograd, an industrial city in southern Russia, killing at least 15 people and injuring dozens, officials said.

No group claimed responsibility for Sunday's deadly bombing, one of several to hit southern Russian in recent months as the nation prepares for the Winter Olympics in Sochi in February.

Shortly before 1 p.m., authorities said, a person initially identified as a woman approached a metal detector frame at the railway station's entrance, stopped, and detonated the explosives after a police officer approached.

"When the suicide bomber saw the metal detector frame and saw the policemen on duty as she entered the railway station, she got nervous and her behavior seemed suspicious to the policemen," Interior Ministry spokesman Andrei Pilipchuk told the Russia-24 television news network. "[Police Officer] "Dmitry Makovkin started in her direction at a fast pace, and at that moment the explosion rang."

Makovkin died on the spot, and six police officers were among the injured, Pilipchuk said.

Authorities later said the bomber might have been a man. The attacker's remains were found and DNA will be tested, the official RIA Novosti news agency said.

At the time of the bombing, the station was unusually crowded, authorities said. Bad weather had grounded flights for three days at Volgograd's airport, forcing more people to take trains, and many people were there to await arriving trains. Had the bomber entered the main hall, the number of casualties could have been much higher

The power of the explosion was equal to about 22 pounds of TNT, officials said.

Sergei Bazhenov, Volgograd regional governor, told Russia-24 that two of the injured were in critical condition.

Moscow Mayor Sergei Sobyanin said that clinics in the capital, about 600 miles to the north, were ready to receive the injured and that an Emergency Situations Ministry plane was on its way to get them.

Volgograd suffered a similar attack in October when a female bomber struck a passenger bus, killing eight and injuring 33 people. She was identified as a member of an underground resistance cell in the republic of Dagestan, in the North Caucasus region, officials said.

In addition, three people died Friday when a car filled with explosives blew up near a traffic police station in the city of Pyatigorsk, also in the North Caucasus. Two explosions were reported Sunday near a grocery store in the Dagestani city of Derbent; five people were injured.

The Volgograd region is close to the North Caucasus and Sochi, where the Olympic Games are set to begin Feb. 7.

Volgograd is close to the troubled Caucasus region, where Chechen rebel leader Doku Umarov has vowed to use "maximum force" to prevent Russia from staging the Winter Olympics, which he called "satanic games held on the bones of our ancestors."

Security appears to be a major concern of the Olympic organizers.

"There are more police officers in the streets of Sochi than residents now with a police car or two parked at every intersection," Oleg Rubezhansky, editor in chief of the local newspaper, Mestnaya, said in a phone interview. "People are afraid to drive their cars anywhere in or outside the city because they are stopped and cars searched more than once during even a short ride."