A rebel-linked Web site said Friday that Chechen warlord Shamil Basayev (search) had claimed responsibility for the power outage that plunged Moscow into chaos two days earlier.

"Our sabotage units delivered a major blow to one of the most important life-support systems of the Russian empire," the Kavkazcenter site quoted Basayev as saying in an e-mail.

Russian officials have blamed worn-out equipment for Wednesday's power failure, which began with an explosion and fire at a 40-year-old substation.

The Federal Security Service declined comment on Friday's claim and telephone calls to the Industry and Energy Ministry were not answered.

But Industry and Energy Minister Viktor Khristenko was quoted earlier in the day as rejecting speculation that a terrorist act was responsible for the blackout.

"I think that this is not a terrorist act. We are just using old equipment, from 1958, which needs to be replaced," Khristenko told the RIA-Novosti news agency, the Gazeta.ru news Web site reported.

The blackout affected millions of people in Moscow and the surrounding region, stranding subway riders and trolley passengers, and leaving entire neighborhoods in the dark.

The outage spread in a cascade effect, reaching as far as the Tula region, 120 miles to the south. Electricity was restored across the capital Thursday.

"The Russian authorities are willfully lying, hiding the real reason for the 'technological catastrophe,' as well as trying to cover up the very serious consequences of this special operation we carried out," Basayev said according to the Web site, which he has used in the past to claim responsibility for terrorist acts.

Basayev is Russia's most-wanted man, and is seen as the driving force behind the Chechen insurgency since Russian security forces killed guerrilla leader Aslan Maskhadov (search) on March 8.

Basayev has claimed responsibility for many of Russia's most deadly terrorist attacks, including the 2002 Moscow theater hostage-taking and September's school siege in southern Russia in which more than 330 people died.

Russia's atomic energy agency issued a statement Friday denying that a malfunction had occurred at any nuclear facility on Wednesday or the following days. The statement apparently came in response to rumors of an accident at a reactor in Obninsk, about 60 miles southwest of Moscow.

"All Rosatom (state atomic energy agency) facilities, including at Obninsk ... are working normally," the statement said, adding that the power outage had no "substantial influence" on Rosatom enterprises.

The head of the nation's electricity monopoly, Anatoly Chubais, has come under heavy criticism over the power outage. Prosecutors interrogated him about the blackout for four hours Thursday, news agencies reported, stressing that he was called as a witness.

In March 2004, police discovered a powerful bomb in an apartment building near Moscow and disposed of it without casualties. Russian newspapers at the time quoted security officials as saying the flat had likely been leased by a group headed by Basayev, with the purpose of blowing up gas pipes, power lines and other industrial infrastructure around the capital.