Russia has failed to rein in Chechen kidnappers

"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," it said.

"MSF urges that whoever may be holding their colleague will respect his physical and mental integrity and will release him unharmed."

MSF said its other staff in the convoy managed to get away safely.

Russian officials said a search had been launched for Mr Gluck.

Russian criticism

The convoy is said to have been travelling without the authorisation of the military commandant of Chechnya, when it came under automatic weapons fire from a Zhiguli car carrying the hostage-takers.

Russia's military commander in the breakaway Caucasus republic, General Ivan Babichev, said Mr Gluck had been working in Chechnya without official permission.

"Part of the blame for this tragedy lies with the international organisation itself," he said.

MSF rejected the criticism, saying it always gave advance notice when sending aid convoys to Chechnya.

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.