MOSCOW – Two female suicide bombers blew themselves up Monday in twin attacks on Moscow subway stations jam-packed with rush-hour passengers, killing at least 37 people and wounding 65, officials said. They blamed the carnage on rebels from the Caucasus region.

The blasts come six years after Caucasus Islamic separatists carried out a pair of deadly Moscow subway strikes and raise concerns that the war has once again come to Russia's capital, amid militants' warnings of a renewed determination to push their fight.

Chechen rebels claimed responsibility for a deadly bombing late last year on a passenger train en route from Moscow to St. Petersburg. Last month, Chechen rebel leader Doku Umarov warned in an interview on a rebel-affiliated Web site that "the zone of military operations will be extended to the territory of Russia ... the war is coming to their cities."

The first explosion took place just before 8 a.m. at the Lubyanka station in central Moscow. The station is underneath the building that houses the main offices of the Federal Security Service, the KGB's main successor agency.

About 45 minutes later, a second explosion hit the Park Kultury station, which is near the renowned Gorky Park.

"I heard a bang, turned my head and smoke was everywhere. People ran for the exits screaming," said 24-year-old Alexander Vakulov, who said he was on a train on the platform opposite the targeted train at Park Kultury.

"I saw a dead person for the first time in my life," said 19-year-old Valentin Popov, who had just arrived at the station from the opposite direction.

Prime Minister Vladimir Putin, who built much of his political capital by directing a fierce war with Chechen separatists a decade ago, vowed Monday that "terrorists will be destroyed."

The iconic Moscow subway system is one of the world's busiest, carrying around 7 million passengers on an average workday, and is a key element in running the sprawling and traffic-choked city.

Russian TV showed amateur video from inside the Lubyanka station of wounded and possibly dead victims sitting and lying on the floor. The train platform was filled with smoke.

Outside both stations, passengers flooded out, many of them crying and making frantic calls on their cell phones. The wounded were loaded into ambulances and helicopters, some with their heads wrapped in bloody bandages, as sirens wailed.

The last confirmed terrorist attack in Moscow was in August 2004, when a suicide bomber blew herself up outside a city subway station, killing 10 people. Responsibility for that blast was claimed by Chechen rebels.

Russian police have killed several Islamic militant leaders in the North Caucasus recently, including one last week in the Kabardino-Balkariya region. The killing of Anzor Astemirov was mourned by contributors to two al-Qaida-affiliated Web sites.

The killings have raised fears of retaliatory strikes by the militants.

Emergency Minister Sergei Shoigu said the toll was 37 killed and 102 injured, but he did not give a breakdown of casualties at each station.

In a televised meeting with President Dmitry Medvedev, Federal Security Service head Alexander Bortnikov said body fragments of the two bombers pointed to a Caucasus connection. He did not elaborate.

"We will continue the fight against terrorism unswervingly and to the end," Medvedev said.

Neither he nor Putin, who was on an official trip in Siberia, announced specific measures and it was not clear if Russia has new strategies to unleash in the Caucasus, where violent separatism has spread from Chechnya into neighboring republics.

Although the Russian army battered Chechen rebels in massive assaults a decade ago, the separatists continue to move through the region's mountains and forests with comparative ease and launch frequent small attacks.

New York's transit system beefed up security as a precaution following the Moscow bombings. A spokesman for New York's Metropolitan Transportation Authority, Kevin Ortiz, said the agency has a "heightened security presence," but declined further comment.

The agency is in charge of New York City buses and subways, as well as suburban trains, and bridges and tunnels.

The Moscow blasts practically paralyzed movement in the city center as emergency vehicles sped to the stations.

In the Park Kultury blast, the bomber was wearing a belt packed with plastic explosive and set it off as the train's doors opened, said Vladimir Markin, a spokesman for Russia's top investigative body. The woman has not been identified, he told reporters.

A woman who sells newspapers outside the Lubyanka station, Ludmila Famokatova, said there appeared to be no panic, but that many of the people who streamed out were distraught.

"One man was weeping, crossing himself, saying 'thank God I survived'," she said.

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Associated Press Writers Jim Heintz, Lynn Berry and Mansur Mirovalev in Moscow contributed to this report.