A giant Russian army transport helicopter has crashed in Chechnya with the estimated loss of 85 lives.

Russian media say the Mi-26 came down in a mine-field near Grozny after the pilot reported a fire in the engine compartment and radioed that he was attempting an emergency landing.

Of the estimated 132 people aboard, at least 32 are known to have survived and are in hospital in nearby Khankala, Russia's main military base in Chechnya.

Chechen rebels are reporting their forces shot down the helicopter but Russian officials have still to confirm the cause of the crash.

The helicopter plunged some 200 metres (600 feet) into a mine-field on the perimeter of Khankala, where it had been due to arrive from Mozdok air base in Russia's North Ossetia region.

Sappers had to clear a path through the mines as smoke and flame billowed from the wreckage, local military sources were quoted as saying.

Russia's ORT television channel said it was the worst air crash in the history of the Russian army.

'Disaster'

The Russian Defence Ministry has not officially confirmed the heavy death toll but President Vladimir Putin talked of a "disaster" as he set up a commission to investigate.

According to the ministry, there was no rebel involvement and the helicopter pilot did not report a hit.

Helicopter crashes in Chechnya

Feb 2002 - Eight killed Jan 2002 - 14 senior Russian officials killed Sept 2001 - 10 passengers and three crew killed Aug 2001 - two killed July 2001 - nine troops killed Feb 2000 - 15 killed

But the Chechen separatist news agency Kavkaz Centre reported the crash as the "greatest act of sabotage by Chechen fighters in two years".

Russia's Interfax news agency and sources with links to the Chechen rebels both said the helicopter had been shot down using either rockets or machine-gun fire.

There have been six helicopter crashes in Chechnya in recent years, almost all of them due to technical faults.

The crash follows a surge in rebel action including attacks late last week which killed nine servicemen and five civilians.

The war has been going on for nearly three years, but the Russian Government maintains that only isolated groups of rebels are holding out against federal forces.