Russian Defence Minister, Igor Sergeyev, said the military had the full backing of President Boris Yeltsin in its mission to establish control of the rebel republic.

The UNHCR's Lyndall Sachs: "We are heading towards catastrophe"

The move has led to speculation that Russian forces may soon try to storm the capital Grozny, which has been under siege for weeks.

The statement is a further blow to international efforts to get Russia to pursue a diplomatic solution to the conflict.

Russian President, Boris Yeltsin, has interrupted a holiday to return to Moscow for talks with the Prime Minister, Vladimir Putin. Russian media reports said they discussed the situation in the North Caucasus.

The BBC's Richard Lister: A frank discussion

US President Bill Clinton on Tuesday met Mr Putin to highlight the political and humanitarian costs of the conflict.

Some 4,000 people are trapped in freezing weather on the Russian-held border with the republic of Ingushetia, as they attempt to escape the Russian onslaught. Only 20 people were allowed through on Wednesday, before troops again closed the crossing.

Refugees are stranded at the border in freezing weather

So far this week, only around 300 have been allowed to leave the rebel republic despite Russian claims that the border is open.

One woman was killed on Tuesday after a crowd made a desperate push forward in an attempt to cross the border.

By Wednesday afternoon, five buses had crossed the checkpoints carrying refugees both ways - but correspondents say it was too little to have an impact on the huge numbers on either side of the frontier.

Federal troops shut the border almost two weeks ago after nearly 200,000 civilians fled to Ingushetia.

A United Nations mission is heading to the area to assess the humanitarian situation. Russia's Emergencies Ministry said the UN team had left on Wednesday for the Russian republic of Dagestan, east of Chechnya, and would go to Ingushetia later.

Closing in on Grozny

The BBC's Lindsay Marnoch: "Tank after tank after tank"

Inside Chechnya, increasing numbers of people are trying to flee Grozny. Russian forces are reported to have taken up positions 4km (2.5 miles) from the city.

Correspondents say refugees are reporting an increasing number of civilian casualties.

Russia says it is aiming its fire only at guerrilla bases, but there are reports that several attacks hit civilian targets - including a Red Cross refugee convoy which was hit by missiles from Russian warplanes last week, after it was turned back from the frontier.

The BBC's Orla Guerin in Moscow says the statement that federal troops will try to re-take Chechnya is not unexpected, and confirms Moscow's real intentions to launch a full-scale offensive in the region.