Russia has failed to rein in Chechen kidnappers

"We have suspended our work in Chechnya and our international staff are now in Ingushetia," said Diderik Van Halsema, a spokesman for MSF.

He said the move was a precaution and the organisation was reviewing the situation.

"MSF is extremely concerned about the fate of its colleague and is outraged at this direct attack on a clearly marked humanitarian convoy that was delivering medical assistance to the Chechen population," a statement from the organisation said.

The UN, which did not have any international staff in Chechnya at the time of the kidnap, has halted a World Food Programme shipment to Chechnya and suspended its operations inside Chechnya on Wednesday.

Highland stronghold

Russian officials have blamed separatist guerrillas for the kidnap and are scouring the region for Mr Gluck.

At present nothing is known of his whereabouts, an officer the Russian Interior Ministry Department in the Chechen Republic told the news agency Itar-Tass.

Another car, carrying an American working for Action Contre La Faim (Action Against Hunger), Jonathan Littel, managed to smash its way through the ambush, although Mr Littel was lightly wounded.

Officers of all the provisional and permanent police stations of Chechnya are taking part in the search operation.

According to existing information, Mr Gluck may be held by the guerrillas at one of the highland bases in the southern part of Chechnya.

Chechen rebels belonging to a group controlled by a field commander called Akhmadov are being blamed for the kidnap and the Russian authorities expect a ransom demand soon.

Denial

But a spokesman for the rebels, Movladi Udugov, has denied these allegations, Tass reported.

"Akhmadov has no link to this incident. We have no need to bother with Americans, we have no money problems," he said by telephone, from an undisclosed location.

Russian officials have accused Mr Gluck of entering Chechnya without proper authorisation, but MSF has rejected the allegation.

In recent years Chechnya has seen a spate of kidnappings, including the beheadings of four employees of a British telecommunications company.

Russia launched a new military assault on Chechnya in October 1999, since when some aid workers and journalists have been returning to the republic.