Nato had threatened air strikes if the Serbs did not sign an agreement by 1100GMT on Saturday. But with Russia openly opposed to military action and France expressing reluctance, the deadline was extended to Tuesday.

The Russian Foreign Minister, Igor Ivanov, reiterated Moscow's opposition to strikes on Saturday. "Military actions will not resolve the Kosovo conflict," he said.

And Prime Minister Yevgeny Primakov called the UK Prime Minister Tony Blair on Saturday to encourage an extension to a deadline for talks.

The joint chairmen - UK Foreign Secretary Robin Cook and his French counterpart Hubert Vedrine - believed progress had been made and the US reluctantly supported the extension, despite pessimism about the prospects of a satisfactory outcome.

A White House official said: "We felt we were in a position we couldn't say no [to the extension in the talks]. Under the circumstances both sides felt that more time was required. We felt it appropriate to allow this to continue."

US stands firm

Cruise missiles would be the first wave of proposed strikes

The main sticking point in the talks is whether Nato peacekeepers will be stationed in Kosovo.

Serbian President Milan Milutinovic indicated that Serbia would allow foreign troops once a political agreement is signed.

"We expect nothing less than a complete interim agreement including Belgrade's acceptance of a Nato-led force," said US Secretary of State Madeleine Albright.

A senior US official said Washington did not expect the Serbs to agree to a complete peace deal including a Nato-led force in Kosovo.

Creeping conflict

The US fears that the conflict in Kosovo could spill into neighbouring countries, including Nato members Greece and Turkey.

"The conflict in Kosovo has no national boundaries," Under-Secretary of State Thomas Pickering testified to Congress earlier this month.

Washington fears that a flood of Kosovar refugees could threaten stability in Nato member states, and that attacks on Kosovar Albanians could spread to neighbouring Albania, and then on to the largely Albanian population of Macedonia.

With such a scenario on the borders of three Nato countries, the US is keen to head off a conflict that could become difficult to contain.

Hard sell at home

Congress wants a say on troops in Kosovo

Under Nato plans, about 4,000 Americans would serve in a peacekeeping force totalling 28,000. US support remains mixed in increasing a military presence in Yugoslavia.

Some in the US House of Representatives oppose the troop deployment without the consent of Congress.