The US special envoy, Mr Richard Holbrooke, is to make a last effort this evening to persuade President Slobodan Milosevic of Yugoslavia to halt aggression in Kosovo or face NATO air strikes.
His last-ditch mission was announced shortly before the deaths of four Serb policemen in the Kosovar capital, Pristina, brought the situation on the ground to flashpoint.
The US Secretary of State, Ms Madeleine Albright, announcing the mission here yesterday, said Mr Holbrooke "will emphasise to President Milosevic that NATO air strikes are being prepared".
"He will make clear that Milosevic faces a stark choice: to halt aggression against Kosovar Albanians and accept an interim settlement with a NATO-led implementation force or bear the full responsibility for the consequences of NATO military action," Ms Albright said.
President Clinton was briefed on the situation on Saturday. At his press conference the day before he said the "threshold" for triggering NATO action had already been crossed in Kosovo by the Serbian forces of Mr Milosevic. He warned that "hesitation is a licence to kill" and that "if we and our allies do not have the will to act, there will be more massacres".
Mr Clinton's National Security Adviser, Mr Sandy Berger, said on CBS Face the Nation yesterday that Mr Holbrooke was going to meet Mr Milosevic today "one final time to make clear to him that he faces a very stark choice".
"He can move to the path of peace or he can face punishment from NATO. . . In this period, Ambassador Holbrooke, with the smell of exhaust fumes in the air from the aircraft, will see one final time if Mr Milosevic is prepared to move down a different path," Mr Berger said.
Asked when the bombing might start, Mr Berger refused to give any information. "NATO will act at a time of its own choosing," he said.
There has been speculation that air strikes will not take place during the visit to Washington this week of the Russian Prime Minister, Mr Yevgeny Primakov, who arrives tomorrow. Russia has made clear it opposes NATO action against Yugoslavia.
A Foreign Office spokesman in London said Mr Holbrooke would meet the British Foreign Secretary, Mr Robin Cook, and the French Foreign Minister, Mr Hubert Vedrine, in Brussels before going to Belgrade to discuss the planned meeting with Mr Milosevic. The US envoy would contact them again on his return from Belgrade so the co-chairmen of the now-halted Kosovo peace talks could reach decisions on "the next steps".
The US Congress is due to debate the use of US forces in NATO air strikes today. Some senators are expressing concern that the Clinton Administration does not have clear goals for launching attacks which could result in the loss of US pilots.
Republican Senator Jon Kyl, of Arizona, said yesterday that "to simply bomb at this point without any strategy is not a good thing for the US or NATO to do". He added that air strikes alone would likely not make Yugoslav forces withdraw from Kosovo.
Reuters adds from Pristina: Four Serbian policemen were shot dead in a drive-by ambush in Pristina last night, Serb sources said.
Shortly after the attack, in which at least one unidentified person was wounded, masked Serbian police with automatic weapons raced in armoured personnel carriers into an eastern district of Pristina in pursuit of the gunmen.
It was the bloodiest attack of its kind in memory in Pristina, which like the rest of Kosovo has an overwhelmingly ethnic Albanian population but has been spared warfare raging within 20km to the north and west.