Russian aircraft, artillery and rocket launchers pounded Grozny on Friday, but failed to dislodge Chechen rebel fighters from the capital.

Russian soldiers in the suburbs of Grozny continued to battle with the Chechen militia, reportedly making little progress towards the centre of the city on the seventh day of their offensive.

"All Russian attempts to reach the city centre have failed," said Mumadi Saidayev, chief of staff of the Chechen forces.

"In some areas, we have managed to push the Russians back. We have left some quarters on the outskirts because they were difficult to defend."

The city centre is still coming under heavy artillery fire from Russian posts on heights surrounding Grozny.

A chemical cloud smelling of ether covered Russian positions in the suburb of Khankala on Friday morning, after a Chechen mortar attack.

On Thursday, 15 oil wells were reported to be burning on the outskirts of the city, blackening the air above the suburbs.

As many as 40,000 civilians are believed to be trapped in Grozny, living mostly in basements with little food or heat.

Air strikes

Another 200,000 refugees are in neighbouring Ingushetia.

Russian Su-24 and Su-25 bombers and Mi-24 helicopter gunships made 83 sorties around Chechnya over the 24 hours to Friday morning, according to Russia's military command.

Air attacks targeted the southern mountains between Grozny and the border with Georgia, with 25 rebel bases, five communications stations and four anti-aircraft systems destroyed, according to the Russians.

A Chechen spokesman said his forces had tight control over Grozny and were inflicting heavy casualties - up to 1,000 soldiers in the last few weeks.

Chechen President Aslan Maskhadov denied rumours that rebel fighters were planning to pull out of the city.

"The military initiative rests entirely in the hands of the defenders of Grozny," he said.

Both sides said they were expecting large-scale fighting over the New Year period, with the Chechens hoping to catch celebrating Russian troops by surprise.

Russian Interior Ministry troops have been ordered to strengthen protection of their bases.

In Moscow, Prime Minister Vladimir Putin has once again defended Russia's campaign in Chechnya as a crusade against terrorism and denounced the West for meddling in Russian internal affairs.

"Russia is facing an insolent challenge from international terrorists in the North Caucasus, and we simply must defend the Russian state and bring the region to order," he said at a Kremlin New Year's party on Thursday.

"We do not allow trampling of the national pride of Russians," he said.

The Russian foreign ministry has said seven foreign journalists detained by Russian forces near Grozny on Wednesday did not have the proper documents to be working in the combat zone.

The press attaches of the US, British and Spanish embassies were called to the foreign ministry and told that further such incidents could result in journalists losing their accreditation, the ministry said in a statement.

The journalists were held for nine hours, interrogated and released.

The British embassy in Moscow is warning all UK journalists in Russia against travelling to the war in Chechnya.

The US State Department also advised journalists that travel to Chechnya was extremely dangerous and urged those in the northern Caucasus to depart immediately.

Embassy officials in Moscow were called into the Russian Foreign Ministry on Thursday to be told of the dangers in the wartorn region.

The ministry said it was concerned that journalists were venturing into military zones where they could be at risk of kidnap, injury or death.

It also stressed the importance of journalists getting proper accreditation before travelling to Chechnya.