SERBIA says it has a former Kosovo rebel witness who allegedly took part in removing the heart of a Serb prisoner for the international black market in organs during the 1990s Kosovo conflict.

"We have a witness who testified about a medical procedure, done in northern Albania, that consisted of harvesting organs from Serbs kidnapped during the 1998-99 conflict in Kosovo," Serbia's war crimes prosecutor Vladimir Vukcevic told AFP.

"He described a surgery harvesting a heart from a Serb prisoner at a location near (the northern Albanian town of) Kukes in the late 1990s," and transporting the organ to the Rinas airport near the capital Tirana, the prosecutor said.

It was not immediately clear if the patient was dead or alive when the operation started, and the prosecutor would not give any more details.

The witness told prosecutors he received special medical training in how to harvest organs and described the operation he took part in "in detail", according to the prosecution.

He added the heart "was sold on the black market", Mr Vukcevic said.

The prosecutor would not give any more details about the identity of the witness, other than to say he was a former KLA member currently under strict protection measures.

Claims of organ harvesting by the Kosovo Liberation Army (KLA) during and after the 1998-99 conflict are being investigated by the European Union.

Council of Europe rapporteur Dick Marty alleged in a hard-hitting 2010 report that senior KLA commanders - including current Kosovo prime minister Hashim Thaci - were involved in organised crime.

The group carrying out organ trafficking during and after the conflict with Serbian forces was closely linked to Mr Thaci, according to Mr Marty.

The report said that organs were taken from the bodies of prisoners, many of them Serbs, held by the KLA in Albania at the time.

Mr Thaci and his government as well as Albania have denied the accusations and condemned Mr Marty's report.

"We have been investigating and checking his claims for more than a year and we estimate that the information this witness has given is true," Mr Vukcevic said.

Following Mr Marty's report, the European Union named US prosecutor John Clint Williamson to conduct a probe.

Refusing to reveal more details for the moment, Mr Vukcevic said he expected "that the witness' testimony will help prosecutor Williamson's probe".

The wartime organ harvesting case is believed to be linked to the so-called Medicus affair, another case of organ trafficking at a hospital in the Kosovo capital Pristina.

Seven people, mostly doctors, are on trial before an EU-run court in Kosovo on charges of illegally transplanting organs at the Medicus Clinic.

The case came to light in 2008 after police opened an investigation into the collapse of a young Turk at the Pristina airport following a kidney donation to an Israeli man.

In his report Mr Marty said there are "credible, convergent indications" that the wartime organ trafficking is "closely related" to the Medicus case.

The allegations of organ harvesting by the KLA were first made public in an April 2008 book by former UN chief war crimes prosecutor Carla Del Ponte.

She said hundreds of victims, mainly Serbs but also other non-Albanians, were kidnapped in Kosovo in the final stages of the war and taken to prison camps across the porous border with Albania, citing unnamed UN officials and journalists as her sources.

The claims were initially investigated in March 2004 by a forensic team of the UN mission in Kosovo (UNMIK), which found "no conclusive evidence" for such charges, according to a copy of the confidential report obtained by AFP in late 2008.

But Jose-Pablo Baraybar, the former chief of the UNMIK Office on Missing Persons and Forensics who headed the 2004 team, told AFP at the time that the case warranted further investigation and that, as a forensic pathologist, he believed organ trafficking there was "probable... at the very least possible".

Kosovo will gain full sovereignty on Monday in accordance with a decision by the International Steering Group which has overseen the territory since it unilaterally broke away from Serbia in 2008.

Belgrade fiercely rejects Kosovo's independence, recognised by some 90 countries, including the United States and most EU member states.