Russia's FSB intelligence agency, the former KGB, announced last week that it assassinated Saudi-born Chechen field commander Khattab, a close ally of Basayev, in an undercover operation in March.

The Chechen rebels confirmed Khattab's death Monday, saying that the FSB had slipped him a poisoned letter delivered by someone he knew personally.

Raising the possibility of a second high-profile assassination of a Chechen guerrilla leader, the ITAR-TASS news agency quoted Kvashnin as saying that Basayev was dead, although his body was not found.

But the army chief later said that the only indication he possessed of the Chechen commander's death was that Basayev's voice had not been intercepted on rebel radio communications for six months, reported Agence France-Presse (AFP).

"It is possible that Basayev is also no longer (alive), but we have no facts to back this up," Interfax reported him as saying.

"When we have proof, we will tell you. Basayev hasn't been heard of either in action or on the radio for half a year," added Kvashnin.

The Chechen leadership dismissed the claim as rubbish. "This is just drunken ravings by Kvashnin," a spokesman for Chechen President Aslan Maskhadov told AFP by telephone.

Meanwhile, Kvashin's own military commander in Chechnya, General Vladimir Moltenskoi, as well as the FSB's top man in the independence seeking republic, said there was no reason to suppose Basayev was dead.

"There is other information that he may still be hiding in one of the bases in the Vedeno gorge," (in Chechnya's southern mountains), said Moltenskoi.

The head of the FSB in Chechnya, General Sergei Babkin, for his part told Interfax that the intelligence agency "has no information to suggest the liquidation of field commander Shamil Basayev."

The Russian military, which until Khattab's assassination failed to kill or capture any of the leading Chechen leaders since the start of the current war in October 1999, claimed, several times in the past, that Basayev was killed.

Basayev, 37, became Russia's public enemy number one following the 1994-96 Chechen war, which led to autonomy for the independence seeking republic.

The Chechen commander, one of the top chiefs in Chechnya who sought to restore a 19th-century Islamic state in the Caucasus, continued fighting despite losing one leg after stepping on a landmine in February 2000.

According to Moscow, Basayev led two rebellions in Russia's southern republic of Dagestan in August and September 1999 and was behind a wave of apartment block attacks across Russia around the same time which killed 293 people.