Kosovo President Hashim Thaci and nine other former separatist fighters have been indicted with crimes against humanity and war crimes charges, including murder.
The charges have been brought by an international court in the Hague, which is investigating their actions against ethnic Serbs and others during and after Kosovo’s 1998-99 independence war with Serbia.
Because of the indictment, Mr Thaci has delayed his trip to the White House in Washington, where he was due to meet Serbian President Aleksandar Vucic for talks on Saturday.
“The President of Kosovo has just informed us that he has cancelled his trip to Washington following the announcement made by the special prosecutor's office," tweeted Richard Grenell, the US envoy for the Kosovo talks.
"I respect his decision not to attend the discussions until the legal issues of those allegations are settled."
The talks will still go ahead, with Mr Vucic and Kosovo Prime Minister Avdullah Hoti, Mr Grenell said.
A prosecutor of the Kosovo Specialist Chambers accused Mr Thaci and the nine others of being “criminally responsible for nearly 100 murders”, involving hundreds of Serb and Roma victims, as well as Kosovo Albanian political opponents.
Other charges include enforced disappearance, persecution and torture, the prosecutor said.
Mr Thaci was a commander of the Kosovo Liberation Army, or KLA, that fought for independence from Serbia.
More than 10,000 people were killed in the war, most of them ethnic Albanians, and 1,641 are still unaccounted for.
It ended after a 78-day Nato air campaign against Serbian troops.
The former ethnic Albanian-dominated province declared independence from Serbia in 2008, which Serbia did not recognise.
The indicted group includes Kadri Veseli, former parliamentary speaker and leader of the opposition Democratic Party of Kosovo.
“The court is trying to stain our liberating war, our aspiration for freedom and independence and legalise the [Serb] crimes in Kosovo,” Bardhyl Mahmuti, a former KLA political representative, told public television station RTK.
The indictment was the first by the special tribunal for Kosovo, which is in The Hague.
The court has been operating since 2015 and has questioned hundreds of witnesses. Kosovo’s prime minister resigned last year before he was questioned.
The indictment is being reviewed by a pre-trial judge who will decide whether to confirm the charges, the prosecutor's office said.
The prosecutor filed the indictment after a long investigation and it reflected his “determination that it can prove all of the charges beyond a reasonable doubt", the office said.
The prosecutor also accused Mr Thaci and Mr Veseli of repeated efforts “to obstruct and undermine the work" of the tribunal.
“Mr Thaci and Mr Veseli are believed to have carried out a secret campaign to overturn the law creating the court and otherwise obstruct the work of the Court in an attempt to ensure that they do not face justice,” the statement said.
“By taking these actions, Mr Thaci and Mr Veseli have put their personal interests ahead of the victims of their crimes, the rule of law, and all people of Kosovo,” it said.
Kosovo politicians resisted and resented the scrutiny of the war crimes court, repeatedly stating that Serb troops went unpunished for massacres and other atrocities during the war.
Tension between the two countries remains high. EU-organised negotiations to normalise their relations started in March 2011 and has produced about 30 agreements, most of which were not observed.
The Washington meeting was set to be the first talks between the two sides in 19 months.
