Erkel has been held for 19 months without any ransom demands

The head of Medecins Sans Frontieres, Jean-Herve Bradol, said he was speaking out because he was concerned for an abducted colleague.

Arjan Erkel, a Dutch national, was kidnapped in Dagestan 19 months ago, but no ransom demand has been made.

Mr Bradol said his kidnapping was aimed at "silencing those criticising conditions in neighbouring Chechnya".

Some very powerful people are involved, including parliamentarians. Everyone knows that Jean-Herve Bradol MSF President

"After 19 months of pragmatism we have decided to break the silence," he told AFP news agency.

"Dagestan and federal officials are implicated in kidnapping affairs.

"We do not make these comments lightly.

"Some very powerful people are involved, including parliamentarians. Everyone knows that."

Mr Bradol accused Russian authorities of leading a pressure and intimidation campaign against those still talking about Chechnya, where, he said, "a crime on an exceptional scale" has been taking place over the past decade.

He said they had seen evidence that Mr Erkel was still alive in October, but believed he was suffering from pulmonary infection and faced execution threats.

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Mr Erkel turned 34 on Tuesday.

He was bundled into a car in August 2002 by three gunmen in Dagestan's capital, Makhachkala.

Medecins Sans Frontieres (MSF) says that the official Russian line - that Mr Erkel was being held by gangsters - was questionable because no ransom request had been made.

One year after the kidnapping, MSF launched an international campaign to put pressure on the Russian government to help secure his release.

It lobbied high-level officials and the media, but no progress was made.

Mr Bradol said negotiations for Mr Erkel's release had been taking place before December, but suddenly the intermediaries withdrew.

He has called on international organisations, including the European Union and the United Nations, to act.

Four years after it launched a second military campaign in Chechnya, Moscow says it has pacified the rebellious republic, but fighting continues.

Human rights groups say more than 400 people were abducted in the region last year.