Lord Robertson, who is soon to take up the post of Nato secretary general, said the European Union should develop the capacity to take independent, timely and informed decisions on crises when Nato was not engaged.

He told a conference in London that Europe must face up to its own security responsibilities.

During the Kosovo crisis it had been the military might of the United States which had given credibility to the diplomatic campaign, he said.

The lesson to learn from Kosovo, he said, was that "Europe should do better".

He said: "Nato remained a cornerstone of our security and defence policy but Europe must be able to field a stronger and more coherent contribution to it.

"We have shown in Kosovo that Europe can be a force for good in the world but we are not doing all that we can."

Defence agreement

Lord Robertson says he will use his new job to forge closer links between Nato and the EU

Lord Robertson's remarks follow the agreement of an EU defence strategy by member states at the Cologne summit in June.

The agreement is intended to make it easier for the union to organise its own military operations independently of the United States and Nato.

It reflects frustration at the limitations of the EU response to the Kosovo crisis.

However, the UK opposition has warned that the move risks alienating the United States.

The Conservatives also fear it could lead to the development of a common European defence force.

'EU must co-operate more'

However, Lord Robertson insisted that EU members should work more closely on defence in the future.

"We must be stronger. We must be more efficient. We must co-operate more fully," he said.

"Only then will Europe have the muscle to underpin our political and economic weight.

"Only then will we truly be able to discharge our responsibilities as one of the richest and most developed group of nations on the planet."

Lord Robertson added that he was looking forward to taking up his Nato post.