Arjan Erkel, a Dutch citizen, was abducted by three gunmen in August in the Dagestani capital Makhachkala and has not been heard of since.

MSF used the occasion of Mr Erkel's 33rd birthday to say that the federal authorities supervising the investigation had failed to provide them with any information about the abduction.

MSF International President Morten Rostrup accused them of failing to demonstrate the necessary "political will".

Nothing has been heard of Erkel for seven months

In a press release the organisation said it was "dismayed by the unwillingness" of the Russian and Dagestani authorities to resolve the case.

"We don't know who is holding him after seven months - if they (the Russians) were taking this more seriously it would have become clearer what is going on," spokesman Martyn Broughton told BBC News Online.

He said MSF was lobbying senior Western officials including the British foreign secretary and Dutch foreign minister to secure Arjan's release.

The absence of any information about Mr Erkel's whereabouts and the failure of his kidnappers to make any demands is highly unusual, according to MSF.

Petition

It often takes three to four months before any information is received about a kidnapping in the region, but it is unprecedented for nothing to be heard for nearly seven months.

The organisation is making a new push to encourage people to sign a petition calling on President Vladimir Putin to secure Arjan's release.

So far it has 150,000 signatures.

Mr Broughton said the failure to solve the case was seriously complicating the work of MSF and other aid organisations in the region.

Many of MSF's regional offices are now staffed only by local employees, he said.

MSF has had to suspend its aid operations in Chechnya several times because of kidnappings, notably after the abduction of regional head Kenny Gluck in January 2001.