Several leaders of Kosovo's 1990s guerrilla army, some of them now senior officials, face possible indictment for crimes against humanity including murder and organ trafficking, an EU probe found Tuesday.

Releasing the first details of a two-year probe, Clint Williamson, the U.S. diplomat and prosecutor heading the inquiry into events after Kosovo's 1998-1999 war, said there was evidence "at this moment (for) ... one indictment that would include a number of individuals."

Kosovo police said Thursday they arrested three ethnic Albanians suspected of setting up a "terrorist organization" as media alleged they were recruited by the Islamic State in Iraq and the Levant (ISIL).

Early on Thursday special police forces carried out an operation coded "Hit" in which three persons were arrested in southern Kosovo over suspicions they were "setting up a terrorist organization and conducting recruitment," a police statement said.

Kosovo police fired tear gas on Sunday to disperse stone-throwing protesters who set alight police cars demanding the removal of a barricade on a bridge linking ethnic Albanians and Serbs in the divided town of Mitrovica.

Six policemen and two photographers were slightly injured as about 1,000 ethnic Albanian protesters pelted the police cordon with stones, police said in a statement.

Kosovo's prime minister called on Thursday for the removal of a blockade of flower pots on a bridge linking ethnic Albanians and Serbs in the flashpoint town of Mitrovica.

The pots were placed across the bridge by Serbs from the northern part of the divided town a day earlier, replacing an already existing barricade of earth and concrete.

A barricade that symbolized the angry refusal of ethnic Serbs in northern Kosovo to merge with the rest of the country was removed on Wednesday after three years.

A bulldozer was brought in to shift the large pile of earth and concrete blocks that lay on the main bridge over the Ibar river in the northern flashpoint town of Mitrovica, an AFP correspondent reported.

The European Union on Thursday agreed to extend its sensitive law and order mission in Kosovo by two years until June 2016.

The 2,000-strong EULEX unit was launched in 2008 just months after Kosovo broke away from Serbia in order to strengthen the rule of law in the territory.

Three Kosovo opposition parties said Tuesday they have united to seek to form a new government in a bid to prevent Prime Minister Hashim Thaci from getting a third mandate after a snap election.

The three parties -- the Democratic League of Kosovo (LDK), the Alliance for the Future of Kosovo (AAK) and the Initiative for Kosovo -- said in a joint statement they wanted to give the tiny country a "government of hope."

Kosovo's snap parliamentary election passed off peacefully on Sunday with Serbs in its restive northern region taking part for the first time in a possible boost for the country's EU hopes. 

Prime Minister Hashim Thaci, an ex-guerilla chief who has dominated politics since the country declared independence in 2008, is seeking re-election but faces a potential backlash in Europe's poorest country over high unemployment and rampant corruption.

Kosovo voted Sunday in snap polls seen as a key test for the country's EU ambitions and for Prime Minister Hashim Thaci, an ex-guerrilla chief who has dominated politics since independence six years ago.

Nearly one in ten people throughout Kosovo had cast their ballots by 11:00am (0900 GMT), the electoral commission said.

Kosovo's president on Thursday called snap elections for June 8 after lawmakers failed to agree on the creation of an army for the former Serbian province.

"I intend to ask from the European Union, in the coming days, to send a mission of observers to closely monitor the electoral process," said President Atifete Jahjaga as she announced the election.