The independent Russian NTV station said casualties among Russian troops were 10 times higher than the official figures.

The news came as Moscow's powerful mayor, Yuri Luzhkov, added his voice to the criticism of the campaign.

The Russian Government's tactics had "produced negative results", the Interfax newsagency quoted him as saying.

He said the Kremlin had not listened to his advice to limit the Russian aim to setting up a security zone.

Meanwhile, conflicting reports are emerging from Chechnya about the fate of a Russian general who disappeared in Grozny last week.

Russian military officials say the body of General Mikhail Malofeyev was found in Grozny, and has been airlifted to a military base west of the Chechen border, before burial in St Petersburg later this week.

But the Chechen rebels say the general is alive and is still being questioned.

Media's mood changes

A BBC correspondent near the Chechen border, Paul Anderson, says that the mood - at least among the non-state media - is changing.

The country's media no longer seems willing to follow the government and military line of reporting battlefield successes and low casualties without question.

An undercover investigation by NTV has reported that up to 50 Russian soldiers are being killed in Chechnya daily.

The figure was compiled from reports from witnesses, morgue officials, railway workers and coroner's assistants.

At least 15 coffins, sometimes more, are being sent to the southern Russian city of Rostov-on-don each night, according to a railway official.

"It's never less than 10, sometimes it's up to 50 a day" he said.

A morgue assistant told NTV that 30 bodies a day passed through his services.

According to official casualty figures five soldiers and 80 rebels were killed in fighting on Sunday.

The total Russian death toll since the conflict began in October is less than 600, according to the Russian authorities.

Marina Fedulova, head of the Association of Soldiers' Mothers, has described this figure as "a gross lie".

Her organisation last week estimated that 3,000 servicemen had been killed so far, based on reports from its regional members.

The Russian Interfax newsagency on Monday reported that there had been 926 Russian deaths, quoting "informed sources in the Russian power-wielding structures".

Tightening the noose

The Russians claim they are slowly tightening the noose around Chechen fighters, who they say are running out of arms and ammunition and have no command and communication systems.

But progress is slow. Russian troops and Chechen rebels fought house-to-house in the frigid ruins of parts of the Grozny on Monday.

Reports suggest that the federal forces are taking a building at a time, where they are able to advance.

In some areas, Russian troops succeed in taking a building during daylight only to lose it in rebel counter attacks overnight.

Click here for a map of Grozny

BBC correspondent Paul Anderson reports that the fiercest fighting is now concentrated around the strategic Minutka square leading to the centre of Grozny.

The square leads to an important bridge across the Sunzha River, which Russian generals have said they are maintaining control of, according to the Itar-Tass news agency.

Air operations

Elsewhere, Russian warplanes and helicopter gunships continued to pound suspected rebel bases, flying more than 100 missions in 24 hours, according to the Interfax news agency.

Air operations were particularly intense in the Argun and Vedeno gorges in south-eastern Chechnya.

Russian forces have captured the large Chechen village of Vedeno, which lies on a strategic rebel supply and escape route and has been under sustained attack for weeks.

But guerrillas still maintain bases in the steep gorges, which are almost impenetrable in winter.

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