A top rebel warlord has claimed responsibility for a bomb attack that killed Chechnya's Moscow-backed leader, Akhmad Kadyrov (search), and pledged to continue attacks against the Russian authorities, according to a statement released Monday.

Warlord Shamil Basayev (search), who now calls himself Abdullah Shamil Abu Idris, claimed responsibility for the May 9 attack in a statement that was posted Monday on a rebel Web site, calling it a "small, but important victory."

He said that other such operations against Russia's so-called collaborators in Chechnya were in the making.

Kadyrov was killed by a bomb at a stadium in Grozny where he and other dignitaries were attending a ceremony marking Victory Day (search), the holiday commemorating Hitler's defeat.

In all, the explosion killed six people and wounded nearly 60, including the top Russian military commander in Chechnya, who lost his leg.

Yuri Rozhin, the head of the Federal Security Service's branch in Chechnya, said Monday that Basayev's possible involvement in Kadyrov's killing was being investigated, but added that the authorities are also looking at other possible culprits, the Interfax news agency reported.

Kadyrov's killing undermined the Kremlin's claims that Chechnya is stabilizing and that it is safe for refugees to return.

Despite Russian forces' superiority in manpower and weaponry, they have been unable to make significant progress in uprooting rebels from Chechnya's southern mountains or from the capital Grozny during the second war in Chechnya.

The first, 1994-96 war ended with the Russian army's withdrawal, leaving Chechnya de facto independent and largely lawless for three years. Russian troops swept back in again in September 1999 following raids on a neighboring province launched by Chechnya-based rebels and apartment building explosions Moscow blamed on the insurgents.

Basayev has taken responsibility for many terrorist acts, including the rebels' seizure of some 800 hostages in a Moscow theater in October 2002 and a recent series of suicide bombings in Moscow and other cities.