August 15, 2007 (RFE/RL) -- A man identifying himself as a member of a Chechen extremist organization says the group is responsible for the August 13 bomb attack on a Russian express train running between St. Petersburg and Moscow.

The man, who identified himself as the deputy commander of Riyad us-Salikhin, told RFE/RL's North Caucasus Service in a phone call that the bombing, which injured more than 60 people, was in retaliation for Russia's role in Chechnya.

The identity of the caller and his claims could not be independently verified.

Riyadus Salikhin, or Gardens of the Righteous, was formerly led by rebel commander Shamil Basayev, who was killed by Russian special forces in July 2006.

The group has been linked to a number of terrorist acts, including the 2002 attack on the pro-Russian Chechen government building in Grozny, and the so-called "black widow" airline and subway suicide bombings in 2004.

The Russian Prosecutor-General's Office says the explosion on the Neva express train was caused by a homemade bomb packed with the equivalent of two kilograms of TNT.

Russian officials say they are looking for two suspects seen on the rail line by passengers prior to the blast.

Reports said experts had drawn sketches of the suspects based on eyewitness descriptions.