An EU prosecutor has indicted 15 former Kosovo rebels on charges of torturing and killing civilians during the 1998-99 separatist war with Serbia.
Many of those indicted are said to be members of the governing Democratic Party of Kosovo.
Lawyers for some of the 15 have rejected the charges. Kosovo war veterans groups said the indictments were politically motivated.
The EU prosecutes war crimes in Kosovo seen as too sensitive for local courts.
Eulex, the EU's Rule of Law mission in Kosovo, said the charges related to crimes allegedly committed at a detention centre run by Kosovo Liberation Army rebels in 1998.
"The defendants are charged with criminal offences of war crimes against civilian population, including torture, mistreatment of prisoners, and murder," it said in a statement.
The detention facility was located in Drenica, the KLA's north-western stronghold in its fight against the armed forces of then Serbian president Slobodan Milosevic.
Eulex did not name the defendants, but reports said they included members of Prime Minister Hashim Thaci's Democratic Party of Kosovo.
Lawyers for two men - Sylejman Selimi, a former KLA commander who is now Kosovo's ambassador to Albania, and Sami Lushtaku, the mayor of the northern town Srbica - have denied their clients were involved in war crimes.
Eulex investigations into former rebels have previously provoked angry protests from ethnic Albanians in Kosovo.
Kosovo's ethnic Albanian majority fought an insurgency against Serb forces in the late 1990s, in which more than 10,000 people were killed and hundreds of thousands driven from their homes.
Nato bombed Serb positions to halt the mass ethnic cleansing and, in June 1999, Kosovo was placed under UN administration.
Kosovo formally declared independence from Serbia in 2008, a move that was opposed by Belgrade. The international community is split over recognition.
The indictments against the 15 former rebels is the third high-profile war crimes case launched by Eulex.
In June, three former KLA commanders were convicted for abusing civilian detainees in a rebel-run prison.
In September, Fatmir Limaj - a former top KLA commander who is a senior Democratic Party figure - and nine other people were acquitted after a Eulex indictment accused them of abusing civilians at a detention centre.