Nato troops raided apartment blocks in a flashpoint Kosovo town yesterday after two days of mass violence the alliance said verged on "ethnic cleansing" of Serbs by majority Albanians.
Almost 1,000 Serbs have fled their homes and sought the protection of Nato-led peacekeepers stationed in the province after riots, gunfire and arson attacks on Serb churches and villages.
"This kind of activity actually almost amounts to ethnic cleansing and it cannot go on," US commander of Nato forces for Southern Europe, Admiral Gregory Johnson, told reporters in Kosovo's capital Pristina.
"That's why we came here in the first place." No fresh hostilities were reported on Friday afternoon. Several countries said they were sending hundreds of additional troops to reinforce Nato peacekeepers and United Nations police trying to restore order.
"It is tense but I am not aware of new incidents or explosions," said a UN police spokesman in Pristina. "It is generally quieter."
So far 31 people, both Serbs and Albanians, have been killed in Kosovo's worst outbreak of violence since 1999, dealing a blow to hopes the UN and Nato can foster lasting reconciliation between the Orthodox Serbs and Muslim Albanians.
The United Nations refugee agency said more bloodshed might provoke a fresh Serb exodus from the province.
"There are not many (ethnic) minorities left in Kosovo - 220,000 have fled since 1999. We don't want to see any more go," UNHCR spokesman Ron Redmond told a news conference in Geneva.
In Belgrade, where the Serb authorities have accused ethnic Albanians of trying to evict remaining Serbs from Kosovo, some 30,000 students marched to protest at "Albanian terror". Some carried banners saying 'New York, Madrid, Kosovo'.
Nato-led KFOR peacekeepers said yesterday they had killed a sniper and raided apartment blocks in Mitrovica.
A loud blast shook a high-rise building in Mitrovica yesterday morning and Nato troops evacuated residents.
Smoke billowed from windows in the building, populated mainly by Albanians, but located in the Serb-dominated northern part of the ethnically divided town.
Reuters reporters on the scene said hundreds of KFOR soldiers remained near the bridge dividing Mitrovica, with several Armoured Personnel Carriers blocking the bridge.
Seven Nato member states hurriedly sent altogether 2,000 reinforcements to beef up the 18,000-strong force.
Germany decided to send 600 more troops, raising the German contingent to 3,800. France pledged to send an extra 400 and Denmark promised an additional 100.
About 150 British troops landed in Kosovo early yesterday, the first of a promised 750 soldiers.
About 150 US troops and 80 Italian Carabinieri arrived on Thursday. Nato-led peacekeepers in neighbouring Bosnia said they had sent an extra 160 Italian and British troops to Kosovo.
Western diplomats and analysts said the violence had made the search for a final status of the province more difficult. Some believed the scale and coordination of the Albanian attacks suggested they were part of their drive for independence.