The Russian news agency Itar-Tass quoted one soldier as saying they were "gradually expanding their zone of control" in the city.

It said the military estimated the operation to capture Grozny might take three to four days.

An earlier drive to seize the city, also scheduled to take several days, ran into trouble over New Year when troops encountered stiff resistance from entrenched rebels.

The military said fierce fighting was taking place on two fronts as other troops fought their way in.

But BBC correspondents in Moscow say there is no independent confirmation of the reports.

A spokesman for Chechen President Aslan Maskhadov told the French news agency AFP that the key Zhukovsky bridge linking east and west Grozny had fallen to the Russians, and that the city was being stormed from all sides.

Russian warplanes have been subjecting Grozny to a relentless bombardment in the last two days, in an attempt to finally break the resistance of the separatist rebels.

Click here for a map of Grozny

An oil refinery and ammunition dumps have been struck and reconnaissance photographs show about 20 separate fires raging across the beseiged capital.

Helicopter gunships have also been attacking Chechen positions along roads and in villages in mountains south of the capital.

A BBC correspondent at the Russian operational headquarters in the region said Moscow was hoping that penetration bombs dropped from the air would destroy Chechen fortifications that have resisted artillery assaults.

Russian TV, quoting the Defence Ministry, said special forces trained in urban warfare were leading the ground assault on Grozny.

A Russian army spokesman said that almost 100 rebels had died in the latest phase of the offensive. The Chechens say 250 Russians have been killed in the last two days.

Critics of Moscow

The attack came as officials from the Council of Europe prepared to visit the North Caucasus to meet regional leaders.

David Russell-Johnston, leader of the delegation, met Russia's acting President, Vladimir Putin, on Monday, but pleas for a ceasefire were dismissed by Moscow.

Mr Putin called on Western nations to judge Russia on the basis of facts, not propaganda.

The delegation will visit Russian-controlled villages in Chechnya, as well as meet Ingushetia's President Ruslan Aushev - a critic of Moscow's policies in the region.

His republic has had to deal with an influx of more than 200,000 Chechen refugees.

The Council of Europe delegation is on a fact-finding mission ahead of a special debate about Chechnya, scheduled for 27 January.

Lord Russell-Johnson says some of the 41 member states are concerned at the killing in Chechnya, but that talk of Moscow's suspension from the body is premature.

Rebel resistance

Thousands of civilians are understood to be trapped in Grozny as the battle rages around them.

Many of them are too old or too frail to leave, and are hiding in cellars hoping to survive the bullets and the bombs.

There are also reports of fierce fighting in the south of the republic. The rebels say they are resisting Russia's onslaught and will continue to do so.

At the weekend, Mr Putin stressed that civilians would not be sacrificed for military gains, because local support would be critical in beating the rebels.

Moscow moved troops into Chechnya last September after blaming separatist militants for incursions into Dagestan and bomb attacks in Russian cities.

Click here to return