The pressure on the US to plan for the use of ground troops in Kosovo has stepped up with visits to Washington from the British Foreign Secretary, Mr Robin Cook, and the NATO commander, Gen Wesley Clark.
Gen Clark is reported to have briefed the Secretary of Defence, Mr William Cohen, and military service chiefs at the Pentagon that while the air campaign is succeeding, it may not be enough to force President Slobodan Milosevic to accept the NATO terms for a return of the Kosovan refugees.
Later, the Pentagon spokesman, Mr Ken Bacon, said Washington wanted a rapid build-up of a NATO force in Macedonia which would be used in Kosovo to secure the return of ethnic Albanian refugees.
"No one can guarantee at this stage that the air campaign will produce all of the objectives by the fall," Mr Bacon said. "We think it will. . .but you have to be open to other possibilities," he said.
Mr Cook has engaged in a media blitz, appearing with the Secretary of State, Ms Madeleine Albright, on a round of TV news and chat shows to emphasise the "unity" between the US and Britain in spite of persistent reports from London of a rift over the use of ground troops. His visit was also portrayed in the British media as aimed at "stiffening the spine" of President Clinton, who was reported in the New York Times as expressing "displeasure" during a phone call to Mr Blair over reports of disunity between them.
Mr Cook played down these reports but when asked what was behind them he could only reply "the papers have to write something".
At closed door sessions with Congressional committees on Capitol Hill, Mr Cook is reported to have urged that if the Serbian forces in Kosovo become sufficiently weakened, NATO should be ready to move in with ground troops. The British Foreign Secretary said on a television programme that he could not "see any sign that the Yugoslav army at the present rate of attrition is going to hold out until August or September".
He told members of Congress that Britain was not advocating a "Normandy-style" invasion of Kosovo. His message was that "this is not the time to lose our nerve", and to be ready to move in to Kosovo when Mr Milosevic shows signs of weakening.
The official US position has been resolutely opposed to any use of ground troops in Kosovo until a political settlement would be agreed with President Milosevic, even though President Clinton shifted position slightly earlier this week when he said that "all options are on the table".
Yesterday in Brussels, NATO told journalists that the prison at Istok in Kosovo, which was struck by a number of NATO missiles yesterday morning, was a legitimate target.
Serbian reports said Kosovan Albanian rebels were held at Istok and that NATO once again targeted civilians by mistake. They claimed that 19 people were killed.
President Clinton yesterday signed a $15 billion war spending bill which Congress approved on Thursday.