Chechen rebel field commander Shamil Basayev has claimed responsibility for the power cut that caused major disruption in Moscow on Wednesday.
Shamil Basayev is linked to a number of terror attacks
A statement on a website with links to the rebels said Basayev's men had attacked an electricity substation, causing the outage.
The cut paralysed public transport and left thousands without power.
Moscow has not responded to the claims, but, at the time, officials said sabotage was not to blame.
In his alleged message to the Kavkaz Center website, Basayev said that on 24-25 May "sabotage groups of mujahideen conducted a successful special operation in territory of Moscow and the Moscow district, having put out of action a power supply system of the Central region of Russia".
"Our sabotage groups have delivered a sensitive blow on one of the most important systems of ability to live of the Russian empire," he said. "The result of the special operation has surpassed our expectations."
He criticised the "lies" from the Russian authorities that the power cut was due to technical problems.
The head of Russia's energy monopoly Unified Energy System (UES), Anatoly Chubais, was questioned by prosecutors over the power cut.
They launched a criminal investigation into the outage, which the company blamed on an explosion and fire at an electricity substation.
Shamil Basayev is the most influential radical figure in the Chechen separatist movement and has been linked to the Beslan tragedy and the Moscow theatre siege.