WASHINGTON (AP) _ The United States urged NATO on Sunday to take a hard look at military options as a fragile cease-fire unraveled in Kosovo.

The White House held a second day of strategy meetings, and Secretary of State Madeleine Albright called allied leaders to discuss bloody developments in the Serb province.

``Clearly, it's a precarious situation,'' James P. Rubin, the State Department spokesman, said as NATO ambassadors prepared to take up the latest crisis in an emergency session in Brussels, Belgium. ``We are going to do all that we can do to preserve the cease-fire,'' he said.

Rubin also denounced as ``complete nonsense'' an accusation by Serbia's deputy prime minister, Vojislav Seselj, that the United States and Britain were training the Kosovo Liberation Army ``for fighting and propaganda.''

In London, a spokesman for the British Foreign Ministry also categorically denied the allegation.

In her consultations, Albright telephoned the foreign ministers of Britain, France, Italy, the Netherlands and Norway, as well as U.N. Secretary-General Kofi Annan. She sent a message to Russian Foreign Minister Igor Ivanov.

At the White House, President Clinton was working on his State of the Union message but was kept informed of Kosovo developments by Sandy Berger, his national security assistant.

Berger's deputy, James Steinberg, was presiding at a late-afternoon meeting of senior officials from the State Department, the Pentagon and other parts of the U.S. government. It was their second meeting in two days on Kosovo. Undersecretary of State Thomas Pickering and Undersecretary of Defense Walter Slocombe were among participants.

``Obviously, it's a very difficult situation and an outrage to everybody,'' David Leavy, the spokesman for the National Security Council, said of the massacres in southern Kosovo of 45 ethnic Albanians. ``We are working for justice and accountability.''

Fighting broke out Sunday in the same area. In a statement, Rubin said, ``The Serb return to the area was a provocation, with the predictable result of instigating these clashes.'' The statement blamed the massacre on Serb security forces for the massacre.

The White House and State Department urged both Serbs and ethnic Albanians to uphold a cease-fire declared in October when American mediator Richard Holbrooke brokered an agreement with Yugoslav President Slobodan Milosevic.

Clinton has termed the latest Serb offensive a clear violation, however. William Walker, the American head of an international force verifying the cease-fire, has called the massacre a crime against humanity.

Milosevic promised in October to pull out special Serb police units and to contain Yugoslav troops. At the time, Milosevic and the Serbs were faced with a threatened bombing campaign as 400 NATO warplanes prepared for action.

That threat was leveled indirectly again Sunday, as Rubin said NATO should review its contingency plans at the Brussels meeting in preparation for dealing with the crisis.

``There should be no doubt of NATO's resolve,'' he said.