Thousands of ethnic Albanians have protested in Serbia against the removal of a memorial to fallen fighters, and dozens of Serb graves in neighbouring Kosovo have been damaged in apparent retaliation.
The monument in the town of Presevo was removed on Sunday by 200 masked Serbian police officers backed by armoured personnel carriers.
It bore the names of 27 ethnic Albanian fighters killed during the 2000 conflict in the Presevo Valley, a spillover from the 1999 war in Kosovo, Serbia's former province.
Authorities in Kosovo said on Monday about 60 gravestones had been demolished at Serb cemeteries in the western town of Prizren and eastern village of Klokot.
Police stepped up security around Serb Orthodox cemeteries.
Police said shots were fired at a memorial to Serbs killed during the 1998-99 war in the western enclave of Gorazdevac and that a monument to second world war communist fighters had been destroyed in the eastern town of Vitina.
In Presevo, a Reuters cameraman saw about 2,000 protesters waving Albanian flags and banners reading "Stop discrimination" and "Europe, open your eyes". Presevo is one of Serbia's poorest regions bordering Kosovo and Macedonia.
Albania and Kosovo, which has an ethnic-Albanian majority, condemned the decision to remove the memorial, erected by the ethnic Albanian-dominated local council.
Serbia, a candidate to join the European Union, said it would not be "humiliated".
Conflict in valley
The Presevo Valley conflict followed a Serbian counterinsurgency war in Kosovo, which ended in 78 days of NATO air strikes in 1999 to wrest control of the province from Belgrade.
Ethnic Albanians in the Presevo Valley fought to unite with Kosovo, but laid down their arms under a NATO-brokered peace deal. Serbia pledged greater rights and economic opportunity for the impoverished south.
However, progress has been patchy.
Kosovo declared independence in 2008, but is not recognised by Serbia.
Kosovo had warned that the removal of the memorial could undermine EU-mediated talks between it and Serbia aimed at normalising relations.
The talks are key to Serbia's bid to join the EU.
The Organisation for Security and Co-operation in Europe, which had been mediating to find a compromise on the memorial, said the decision to remove it had "undercut" the negotiations and appealed for calm.
Albania issued a statement saying the memorial was erected to honour "heroes of the Albanian nation" who had fought against late Serb leader Slobodan Milosevic, toppled in October 2000.
"The racist, anti-Albanian legacy of Slobodan Milosevic is alive and dominates the official policy of Belgrade," it said.
For his part, Ivica Dacic, Serbian prime minister, said: "We are determined not to violate anybody's human, national and civic rights, but no one has the right to humiliate Serbia."