Investigators from a war crimes court have seized thousands of files leaked to a Kosovo veterans' association that revealed details of protected witnesses, the group said Tuesday.
The collection of around 4,000 documents allegedly reveal the identities of witnesses due to testify before the Hague-based court, the association of veterans from the Kosovo Liberation Army (KLA) told local media.
The organisation had announced receiving the classified documents on Monday.
The group's leader Husni Gucati said they were delivered to them by a person "wearing glasses, a mask and a hat".
"He just left the package and ran away," he added.
The tribunal itself, the Kosovo Specialist Chambers (KSC), did not publicly confirm the operation.
But the veterans released apparent court documents marked "strictly confidential" that authorised the seizure at the request of chief prosecutor Jack Smith.
Former commanders from the KLA have gone on to dominate Kosovo politically ever since they helped sever the former province from Serbia in the 1998-99 conflict.
KLA veterans fiercely oppose the work of the Hague-based court and defend their "just" liberation war against Serbian oppression of Kosovo's ethnic Albanian population.
The court operates under Kosovo law but is based in The Hague to protect witnesses, who face threats and heavy pressure not to testify.
President Hashim Thaci -- the KLA's former political chief -- was the first to face accusations from the court's prosecutors in June.
They accused him of being "criminally responsible for nearly 100 murders" in addition to other crimes, in an indictment that needs approval from a pre-trial judge.
Top Serbian military and police officials have previously been convicted in other international courts of war crimes during the conflict that left 13,000 people dead, mainly Kosovo Albanians, and ended with a NATO intervention.
The Kosovo Specialist Chambers is probing allegations that the KLA rebels coordinated a campaign of revenge attacks on Serbs, Roma and ethnic Albanian rivals during and after the war.
Prosecutors said they raced to publish Thaci's indictment because he and others were trying to "obstruct the work" of the court.