Russian Defence Minister Igor Sergeyev has said the final stage of the Chechen war will begin in a few days.

"The final stage of the military phase of the anti-terrorist operation will be held in Chechnya's mountains, where the remaining bandit groups have gathered," he said.

The defence minister said 5,000 to 7,000 rebels have taken refuge in mountain gorges, following their withdrawal from the capital, Grozny.

Heaviest bombs yet

He said the attack would be spearheaded by airborne troops, marines and infantry units which had experience of fighting in the mountains.

On Wednesday Russian aircraft dropped the heaviest bombs yet on rebel groups in the Argun gorge, as a prelude to the ground offensive.

An official at Russia's North Caucasus military headquarters told the Interfax news agency that 1.5-tonne bombs were being used in place of others weighing 250 or 500 kilogrammes.

"The aviation munitions used earlier have proven ineffective in the mountains," he said.

Chechen rebels use the Argun gorge, and the Vedeno gorge further east, as lines of supply.

Russia claims to control the mouths of both gorges.

Russian paratroopers have also been dropped at the top of the Argun gorge.

Chechens have been blowing up paths to prevent the paratroopers coming down the valley, the Itar-Tass news agency reported.

Rebels were also said to have attacked federal troops in Russian-controlled districts near Grozny, including the towns of Argun and Urus-Martan.

Missing journalist

Earlier on Wednesday a Russian television station broadcast the first footage of journalist Andrei Babitsky since he was swapped for Russian soldiers in rebel Chechnya last week.

Mr Babitsky, a Russian citizen who works for the American-funded station Radio Liberty, had earlier been seized by Russian forces after a reporting trip to the Chechen capital.

"It is 6 February, 2000," Mr Babitsky says in the video, suggesting it was filmed after the swap, which the Russian military say was carried out with his agreement.

The video - which was delivered to the BBC office in Moscow on Tuesday and shown on Russian television - shows him talking slowly but clearly for 44 seconds, seated in front of a white wall, a white handkerchief in his hand.

The director of Radio Liberty's Moscow bureau, Savik Schuster, said he still feared for Mr Babitsky's safety.

'Beaten'

According to the radio station's unidentified sources, Mr Babitsky was last seen on Monday - the day after the message was apparently taped - in Gudermes, Chechnya's second city which is under Russian control.

The journalist had been severely beaten, according to the source.

Chechen spokesmen publicly disagreed on Wednesday about Mr Babitsky's fate.

A man often described as Chechnya's representative in Moscow, Sharip Yusupov, said the journalist was alive and in rebel-held territory.

But Chechen Foreign Minister, Ilyas Akhmadov, later said Mr Yusupov did not represent Chechnya, and described his words as a "provocation".

Chechen President Aslan Maskhadov said this week that he did not know where the missing journalist was.