* Ex-guerrillas accused of taking organs from Serb captives
* U.S. prosecutor heading probe under EU auspices
* EU, Kosovo working on creation of ad hoc tribunal
By Fatos Bytyci
PRISTINA, July 21 (Reuters) - An EU-appointed task force will release its findings next week after an investigation into allegations that Kosovo Albanian guerrillas took body organs from Serb captives during the 1998-99 war, Kosovo's justice ministry said on Monday.
Its conclusions could cause waves in Kosovo, where many in power have roots in the guerrilla Kosovo Liberation Army (KLA) that took up arms against Serbian security forces in the late 1990s and eventually won military support from NATO.
The investigation's head, U.S. prosecutor John Clint Williamson, was in Kosovo on Monday and met the president and justice minister.
The ministry said he would issue his findings in a report "during the next week". A government source said Williamson had not discussed its content.
The EU and Kosovo are working on the creation of an ad hoc tribunal, likely to be based in the Netherlands, to try potential suspects.
The investigation was launched after a 2011 report by Council of Europe rapporteur Dick Marty which accused senior KLA commanders of involvement in the smuggling of Serb prisoners into northern Albania and the removal of their organs for sale.
Prime Minister Hashim Thaci, himself a former KLA leader named in Marty's report, has dismissed the accusations as an attempt to tarnish the Kosovo Albanian fight for independence from the government of late Serbian strongman Slobodan Milosevic.
"Kosovo is determined to face these accusations in a credible way and will fulfill its obligations with responsibility and dignity in order to close this chapter, strengthening Kosovo's position in the world," President Atifete Jahjaga was quoted as telling Williamson in a statement.
Serbia's counter-insurgency campaign of 1998 and 1999 eventually drew in NATO, which bombed for 78 days to drive out Serbian forces behind the killings of Kosovo Albanian civilians. Around 10,000 Albanians and just over 2,000 Serbs are believed to have been killed during and immediately after the war.
Kosovo declared independence in 2008 but the EU still plays a guiding role in policing and justice, particularly cases of war crimes.
Efforts to investigate alleged war crimes committed by the guerrillas have run up against widespread intimidation in a small country where clan loyalties run deep and former KLA rebels are revered as heroes. (Editing by Matt Robinson and Angus MacSwan)