Moscow- Medecins Sans Frontieres (MSF), one of the most active charities in Russia's turbulent north Caucasus region, accused Moscow on Wednesday of doing too little to solve an aid worker's kidnapping six months ago.

Morten Rostrup, international president of MSF (Médecins Sans Frontières), said neither federal authorities in Moscow nor local officials in Dagestan, a region bordering separatist Chechnya, had done enough to find Dutch national Arjan Erkel.

"It is imperative that the Russian and Dagestani governments live up to their obvious responsibilities to solve this case: that means treating it with the gravity it deserves," he told a news conference.

Erkel, who was in charge of MSF operations in the region, was seized by three unidentified gunmen in Makhachkala, capital of Dagestan. He was looking after refugees mainly from Chechnya, to the west, where law and order have largely broken down in a decade of conflict between Russian authorities and rebels.

Along with the United Nations, MSF is to suspend its field activities in the region on Thursday as a mark of protest, Rostrup said. Dick Erkel, the father of the kidnapped aid worker, said the family had heard nothing from those behind the abduction. "We do not know where he is, what his situation is," he said. "Is he still alive? Is he in good health? We have only questions."

Rostrup said MSF had never handled a case in which kidnappers remained silent for so long. Abduction as a source of income for criminal groups has been common in the area, with Western aid workers seen as fetching the highest ransoms. The Kremlin declares the "military phase" of its campaign in Chechnya over and says the area is returning to normal.

Authorities say refugees are returning from adjacent areas, though rights groups say they are being forced home. Russian forces come under rebel attack nearly every day. Moscow, which refuses to negotiate with the separatists, has scheduled a referendum for next month on a new constitution anchoring Chechnya within Russia. A top Kremlin aide upheld Moscow's refusal to negotiate despite the appointment of a new, moderate envoy by Chechnya's ousted separatist president, Aslan Maskhadov.

"This representative of Maskhadov - a non-existent president of a non-existent state - no one is going to support relations with him," Sergei Yastrzhembsky, top spokesman on Chechnya, was quoted as saying by Interfax news agency. Salambek Maigov, the new envoy, is a Moscow businessman said to be well connected to politicians and even the military.