Fearing a humanitarian catastrophe, the European Union and the United States ordered Belgrade to stick to its promise to end a fierce drive against ethnic Albanian guerrillas fighting for independence in the Serbian province as thousands of refugees sought shelter in hills and hamlets.
Clashes continued across Kosovo and both key roads leading west from Pristina, Kosovo's provincial capital, were closed and reporters were turned back.
US State Department spokesman James Rubin refused to say what NATO's plans were, but NATO foreign ministers in late May asked military experts to look at possible preventive deployments in Albania and Macedonia which border Kosovo.
"NATO has now approved a range of contingency plans for the use of military force in this regard," Mr Rubin said. "The secretary-general has requested further refinement of those initially approved plans that were approved in recent days.
"I hope President Milosevic understands this," he added.
Mr Rubin said it was up to NATO's political leaders to decide whether action was needed, but noted that the two factors which had made the planning necessary - the refugee dilemma and the risk of regional instability - were getting worse.
The United Nations refugee agency (UNHCR) said that the offensive leading up to the weekend fighting had displaced as many as 30,000 people, taking the total number of refugees and displaced persons to 180,000 since February.
US envoy Chris Hill said Kosovo was on the "edge of a humanitarian catastrophe if refugees don't return to their homes in the next week or two".
"We have an extremely serious situation here. There have been tens of thousands of displaced people in recent weeks and the latest offensive against the KLA has caused even more people to flee from their homes," Mr Hill said.
Mr Hill, Washington's ambassador to nearby Macedonia, has been conducting shuttle diplomacy in a hitherto fruitless bid to get the two sides to talk.
European Union president Austria, which extracted the pledge from Mr Milosevic last week that his offensive was over, urged him in a letter to stick to his promise.
Austrian Foreign Minister Wolfgang Schuessel said he wrote to Mr Milosevic on Friday appealing to him to stop the fighting.
"The most important issue is to tackle the humanitarian situation and then arrange a ceasefire to allow talks to take place," Mr Schuessel said.
Fighting erupted across Kosovo, a Serbian province with a 90 percent ethnic Albanian majority, on Sunday after a couple of days of relative quiet.Reuse content