In the courtyard of NATO's Brussels headquarters, the flags of Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia were raised and their national anthems played by a military band.

Their foreign ministers looked proudly on from a podium, joined by representatives from the existing members -- including US Secretary of State Colin Powell -- and about 200 onlookers in a colourful array of uniforms.

The seven entrants formally joined the North Atlantic Treaty Organisation on Monday when they deposited their accession documents in Washington, opening a new chapter for an alliance long defined by its Cold War role.

"Together with the enlargement of the European Union, today is the clearest demonstration that in Europe, geography no longer equals destiny," NATO Secretary-General Jaap de Hoop Scheffer told the foreign ministers.

Five of the new NATO members are among 10 countries joining the EU on May 1, in another symbolic erosion of Europe's old Cold War frontiers. The other two, Bulgaria and Romania, hope to join the EU in 2007.

The arrival of the new member states comes at a critical juncture for NATO, which was created in 1949 to defend western Europe from the Soviet Union but is now remoulding itself to confront new global challenges.

In the wake of the March 11 attacks in Madrid, the NATO ministers adopted a declaration that pledged to clamp down on terrorism, notably through greater sharing of intelligence.

The alliance also endorsed plans for NATO peacekeepers to fan out from the Afghan capital Kabul to other parts of the turbulent country.

But it struggled to find common ground on Iraq, as Powell ruefully acknowledged.

France and Germany, which bitterly opposed the US-led war, have stressed that a United Nations mandate is essential before they can consent to a NATO mission being deployed in Iraq.

"The US believes the alliance should consider a new collective role after the return of sovereignty to an Iraqi government (planned for July 1)," Powell said.

"But I would think it unlikely that NATO would undertake a formal, collective alliance role before full sovereignty... has been returned to an interim Iraqi government.

"I'm also relatively confident that that government would welcome that kind of assistance from the international community," Powell added.

Individually, 18 of the 26 NATO nations already have troops in Iraq, including six of the seven new entrants.

Romanian Foreign Minister Mircea Geoana said it was high time for transatlantic divisions over the war in Iraq, which last year plunged NATO into its worst-ever crisis, to be put aside.

"All of us, the countries that have suffered under communist dictatorship, have not only a strategic necessity to stabilise Iraq for the sake of the broader region, but also a moral obligation to assist this nation," he added.

The talks with Russian Foreign Minister Sergei Lavrov were another point of controversy blotting the festive atmosphere of NATO's biggest expansion ever.

"We didn't want this enlargement, and we will continue to maintain a negative attitude. It's a mistake," Lavrov told reporters after meeting the NATO ministers.

"The presence of American soldiers on our border has created a kind of paranoia in Russia," he added.

But Latvian Foreign Minister Rihards Piks was defiant.

"The reality of Latvia's history in the last century showed us that the existence of nations is threatened when tyranny prevails," he said at NATO headquarters.

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