And it could have breached international protocols by not trying hard enough to protect civilian lives, said General Sir Michael Rose.

"For 11 weeks the most intensive air campaign in the history of warfare was mounted and we had troops standing by helplessly watching thousands of people brutally murdered and over a million people driven from their homes," he told BBC Radio Four's Today programme.

'Old-fashioned war'

"I wonder what kind of success this is?"

Nato had "simply fought a wrong war", he said.

"It fought a old-fashioned, general war trying to destroy and degrade his (President Milosevic's) military machine but it should have been fighting a humanitarian war," he said.

Countries which took part in the bombing campaign were risking a breach of the Hague and Geneva protocols designed to safeguard civilian lives, he said, "by limiting the flight levels to 15,000ft and not guaranteeing the targets they were engaging were military ones".

Bombers 'held back'

But Nato spokesman Jamie Shea defended the campaign, saying that the alliance could have used far more violent means if it had so wished.

"We didn't want to inflict more suffering on the Yugoslav people than was absolutely necessary," he said.

"Nato very much hoped that the decision to use force would convince Milosevic that the international community was serious, and that therefore he would quickly agree to the objectives we were seeking."