Terror returned to the heart of Russia on March 29, with two deadly suicide bombings on the Moscow subway during the morning rush hour, including an attack at Lubyanka Station beneath the headquarters of the Federal Security Service, the KGB's main successor agency.

The second blast targeted Park Kultury Station, near renowned Gorky Park, on the same line.

At least 39 people were killed and more than 60 wounded in the blasts, the first such attacks in Moscow in six years.

Police have killed several Islamic militant leaders in the North Caucasus recently, which raised fears of retaliatory strikes and escalating bloodshed by the militants.

As smoke billowed through the subway tunnels not far from the Kremlin and dazed survivors streamed out of the vast transportation system, al-Qaida-affiliated Web sites were abuzz with celebration of the attacks by two female bombers.

The bombings followed a warning in February from Chechen rebel leader Doku Umarov that "the war is coming to their cities."

Prime Minister Vladimir Putin, who built much of his political capital by directing a fierce war against Chechen separatists a decade ago, promised to track down and kill the organizers of what he called a "disgusting" crime.

In a televised meeting with President Dmitry Medvedev, Federal Security Service head Alexander Bortnikov said the remains of the two bombers pointed to a Caucasus connection. "We will continue the fight against terrorism unswervingly and to the end," Medvedev said.