Speaking to his NATO counterparts, he recalled that US President George W. Bush was committed to "a mutually-reinforcing relationship between NATO and the EU, grounded in the essential NATO-EU agreements, which underpin it.

"The United States supports a European Security and Defence Policy (ESDP) that improves Europe's capabilities to act and develops in a way that is fully coordinated, compatible and transparent with NATO," he said, according to the text of a prepared speech.

But he warned: "That said, the United States cannot accept independent EU structures that duplicate existing NATO capabilities."

The row over Europe's defence initiative has been simmering for months, ever since a group of four countries opposed to the Iraq war -- France, Germany, Belgium and Luxembourg -- unveiled plans in April for an autonomous military planning cell outside Brussels.

The United States at one stage warned that the plans represented a "significant" threat to NATO, which has long been dominated by the US.

The issue resurfaced last weekend when foreign ministers from France, Germany and Britain, meeting in Naples for talks on the EU's first-ever constitution, said they had agreed draft plans for an autonomous planning cell.

They stressed that the plans would not duplicate NATO capabilities. On Monday this week US Defense Secretary Donald Rumsfeld, also meeting his counterparts in Brussels, sought to downplay the row, saying he was confident the Europeans would agree to arrangements which would not compete with NATO.

Meanwhile, Colin Powell called on NATO yesterday to take on a greater role in Iraq, while also welcoming a "more robust" role for the United Nations.

"We urge the Alliance to examine how it might do more to support peace and stability in Iraq, which every leader has acknowledged is critical to all of us," he said, according to prepared remarks to NATO foreign ministers.

The Iraq war and the diplomatic battles which preceded it sparked the biggest crisis in NATO's 54-year history, as three anti-war countries -- France, Germany and Belgium -- opposed Alliance help for Turkey.

Powell noted that the 19-member Alliance has already provided logistical support to the Polish division of a multi-national force in Iraq, and that 16 NATO members are part of the coalition in the war-scarred country.

He also recalled that UN Security Council resolution 1511 passed on October 16 "encourages the engagement of multilateral and regional organizations in this effort."

Washington has two key objectives in Iraq, he said: a rapid return of sovereignty to the Iraqi people and the creation of a "free, democratic and stable Iraq at peace with its neighbours and within its own secure borders.

"In pursuit of these goals the United States welcomes a greater NATO role in Iraq's stabilization," he said.

"We welcome a more robust role for the United Nations as well," he added.