At least 17 rebels died in the clash, he said. But there was no independent confirmation of that figure.

Russia is sending elite units to the southern mountains

Kremlin spokesman Sergei Yastrzhembsky again ruled out talks with Chechen rebel leaders unless such conctacts concerned the rebels "capitulation".

But he admitted that "with the onset of spring and summer, our difficulties have doubled".

He told Russian ORT television that the rebels were using the foliage in Chechnya's southern mountains as cover.

Russia boosts commandos

Russian President-elect Vladimir Putin meanwhile told ministers he would boost commando numbers in the southern mountains.

Mr Putin, who owes his popularity largely to his tough stance on Chechnya, said that "the special forces will work in the mountain regions where there are still bandits, and they will step up their activities there.

Many Russians support Mr Putin's tough stance on Chechnya

"Russia has no aim in Chechnya other than to eliminate the bandits and rebuild the economy and social sphere" he said.

In the ambush on Sunday, rebels killed at least 15 soldiers, according to the latest toll given by Moscow. The Chechens said 80 Russian troops died in that gun battle.

In the 1994-96 Chechen war separatist forces used the remote highlands as a base to launch deadly guerrilla attacks that forced the Russians to sue for peace and left Chechnya with de facto independence.

Russia now has about 80,000 troops in Chechnya, ranged against a rebel force estimated at 3,000, most of whom are based in the southern mountains.

Maskhadov defiant

Rebel Chechen President Aslan Maskhadov adopted a defiant stance in comments in Friday's edition of the French magazine Le Point.

"I have never ordered a unilateral ceasefire and I will not.

"We agree to stop fighting if the Russians also stop their offensive," he said.

Mr Maskhadov's whereabouts remain a mystery.

The Russian authorities say they have not been in contact with him since an exchange of peace proposals over a month ago.