Facing scathing criticism from MPs of Nato's blunder, Mr Cook told the Commons the attack on the embassy was "a tragic error".

US Defence Secretary William Cohen later blamed the bombing of the Chinese embassy in Belgrade on an old map.

But Mr Cook stressed that such errors were inevitable given the scale of the alliance's military operation and that more civilian casualties were likely.

"I must be blunt with the House - you cannot wage a military campaign of this intensity without mistakes," he said.

"It would be dishonest of me to stand at this despatch box and promise there would be no more mistakes."

The embassy bombing sparked furious protest in China

But the government came under intense attack from the opposition benches, where Conservative MPs wondered how Nato had come to bomb an embassy.

Shadow Foreign Secretary Michael Howard described the attack as "not only a tragic mistake but also an act of gross incompetence".

He asked: "Can you confirm that almost any street map of Belgrade clearly shows the location of the Chinese Embassy?"

The bombing would now make it impossible to persuade the United Nations Security Council - of which China is a member - to agree a resolution backing Nato forces if they crossed into Kosovo to help refugees returning home, the Tories warned.

Independent MP Martin Bell, a former Bosnian war correspondent, also said the bombing had caused widespread dismay and damaged Nato's credibility.

"The greatest military alliance on earth seems in certain respects to be like the gang that couldn't shoot straight," he said.

Air strikes are 'best hope'

Mr Cook said efforts were continuing to find a settlement to the Kosovo crisis based on the blueprint agreed by the foreign ministers of the G8 countries and Russia last week.

But he said: "Our best hope of success on the diplomatic track is by keeping up the military process."

He warned that there "no prospect" existed of a settlement if the Serbs sensed that Nato's resolve was weakening.

Civilian casualties caused by Nato were small in comparison with the killings carried out by Serb forces in Kosovo, Mr Cook added.

He referred to accounts from fleeing refugees of fresh atrocities.

In one village Serb police threw 20 civilians down a well and then tossed in hand grenades, he said.