The US Defence Department said Gen Clark's early departure was not a result of dissatisfaction with his performance during the 11-week war against Belgrade, but part of a general rotation of American senior ranks.

The Nato commander is reported to have had differences with the White House and the Pentagon during the operation.

Correspondents say he consistently urged more aggressive tactics, including the possibility of a ground invasion of Kosovo if the air strikes failed.

His request to use Apache attack helicopters in the air war was turned down by the Pentagon.

When asked if his departure next April was due to his performance in the Kosovo conflict, the 54-year-old general told Reuters news agency: "Not that I know of."

'Praise and respect'

Pentagon spokesman Kenneth Bacon said Gen Clark would be replaced by Air Force General Joseph Ralston, currently vice chairman of the US joint chiefs of staff.

Defence analyst Michael Clark: Gen Clark did not seem aware of the move when it was announced

Mr Bacon said US Defence Secretary William Cohen held Gen Clark in high esteem and believed he had "performed extremely well in this job in a very demanding time".

It was not a question of dissatisfaction, the spokesman added: "We have nothing but the highest praise and respect for the job that Gen Clark has done."

Mr Cohen had recommended Gen Clark for a "high-level ambassadorship," Mr Bacon said.

Successor

US military chiefs felt that the incoming Gen Ralston "would bring the same qualifications to the job that Gen Clark did," the Pentagon spokesman said.

Gen Ralston was "a proven warrior, a proven diplomat and a proven politician," he said. "He has got great skills in all those areas, just as General Clark did."

A veteran of the Vietnam War, Gen Clark became Nato's supreme allied commander in Europe in July 1997. He was also the senior military member of the team that forged the 1995 Dayton peace accords that ended the fighting in Bosnia.

Also leaving his post will be General John Tilelli, commander of the combined UN-US forces in South Korea.