The UN war crimes tribunal cleared Kosovo’s former prime minister of all charges of persecuting Serbs in a 1998-99 separatist war, but sentenced his uncle to six years jail for mistreating prisoners.

Ramush Haradinaj, a former commander of the Kosovo Liberation Army (KLA) considered a hero by Kosovo Albanians, was acquitted of war crimes and crimes against humanity after judges found prosecutors failed to prove a deliberate campaign to kill and expel Serb civilians from Kosovo.

“This is a verdict that strengthens Kosovo. We endured a difficult liberation struggle that cost many lives. Today we are a free and sovereign nation,” Mr Haradinaj said in a statement.

Kosovo’s 90 per cent Albanian majority declared independence from Serbia in February. The UN has run the province since 1999 when Nato drove out Serb forces to halt the ethnic cleansing of Albanians in a two-year war against KLA guerrillas.

Belgrade has branded Kosovo’s secession as illegal, telling the 120,000-strong Serb minority to boycott its institutions. Serbian officials condemned the Haradinaj acquittal.

Mr Haradinaj’s uncle, Lahi Brahimaj, a senior KLA figure, was cleared of most charges but convicted for personally taking part in the cruel treatment of a detainee at a camp, and ordering the mistreatment of another, a perceived collaborator.

A third accused, Idriz Balaj, the commander of the KLA’s “Black Eagles” special unit, was also cleared of all charges of torture, murder, rape and deportation.

Mr Haradinaj was the most senior former KLA guerrilla to be indicted over the war. In the Kosovo capital Pristina the sound of car horns, fireworks and gunfire greeted the verdict, while onlookers cheered and clapped in a packed court public gallery.

But the verdict angered Serbia’s leaders.

“This is a black day for international justice,” said Serbian deputy Prime Minister Bozidar Djelic. “The acquittal is a scandal, a blow to the international justice system.”