The charge comes as Kosovo, a former Serbian province, is waiting to see if an indictment filed by the prosecutors against Thaci will officially be taken up in court.

In an opinion published online, the head of the Specialist Prosecutor Office (SPO) wrote "there is good reason to believe" Thaci has been acting as part of a "larger strategy to undercut the court".

The argument concerns amendments Thaci proposed in August that would give Kosovo's parliament the power to extend the specialist court's mandate for another five years.

Set up with EU-backing in 2015, the Kosovo Specialist Chambers (KSC) operates under Kosovo law but is based in The Hague to protect witnesses from intimidation in a society where many former rebel commanders still dominate politics, like Thaci.

The SPO wrote that its mandate was supposed to continue uninterrupted until "notification of completion is made by the Council of the European Union."

"By suggesting that the temporal mandate of the court requires 'extension' and 'clarification', Mr Thaci implies that its mandate already expired", it said.

"A potential consequence of that position would be the invalidation of all actions taken by the KSC/SPO since that time, notably including any confirmation of the indictment against Mr Thaci himself."

Nearly six months ago prosecutors filed their indictment against Thaci for alleged crimes stemming from his role as political chief of guerilla forces that battled Serbia for independence in 1998-99.

The charges, which include murder, enforced disappearances, persecution and torture, need approval from a pre-trial judge by Saturday.

Prosecutors said they made the news of the indictment public earlier than usual in June because Thaci and others had been trying to "obstruct the work" of the tribunal.

Thaci, 52, has said he would resign if the indictment is confirmed.