Blair, insisting on his credentials as the top US ally, said the EU had no intention of setting up a rival force to NATO after Washington raised concerns about EU defence plans including a new military headquarters in Belgium.

"I'm absolutely the strongest ally the US can have but I know there will be certain situations that, for perfectly good reasons, when the US doesn't want to undertake military operation," he told a news conference in London.

"The EU in those circumstances has got to have the capability to do so."

The United States is seeking reassurance from Europe that its defence plans -- linked to talks on a first-ever constitution for the enlarging bloc -- will not undermine the North Atlantic Treaty Organisation.

EU and NATO diplomats sought to resolve the row at meetings in Brussels this week after a US envoy warned that certain EU defence plans were a "significant threat" to the future of the 19-member NATO alliance.

The United States argues that Europe urgently needs to spend more on military resources, from transport planes to communications, rather than on a new European military headquarters -- a proposal put forward by France, Germany, Belgium and Luxembourg.

"We don't want duplication but we don't competition," Blair said, adding that Europe had no intention of developing a European force in competition with NATO. "We will never do that," he said.

But he added: "It's important to carry on with European defence. I'm not giving up the ability of Europe to have a proper defence capability in circumstances when NATO or America wish not to be engaged."

Washington is concerned that London, its closest ally in the war on Iraq, is softening its opposition to the European defence headquarters plan.

WAR.WIRE