NATO has signed up seven new countries in eastern Europe in a historic expansion that extends the scope of its membership to the Russian border.
The prime ministers of Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia deposited instruments of accession to the North Atlantic Treaty Organisation's founding Washington treaty and brought the number of members to 26.
Five of the seven, Estonia, Latvia, Lithuania, Slovakia and Slovenia, are also due to become full members of the EU at the end of next month.
US Secretary of State Colin Powell called the move historic.
President George W Bush was to meet the leaders of the new NATO members at the White House late today, along with the prime ministers of Albania, Croatia and Macedonia, which also want to join.
Russia again expressed disquiet over the biggest increase in NATO membership since it was founded at the height of the Cold War in 1949.
Russia is particularly concerned about the inclusion of the Baltic states, all former Soviet republics which are still home to many ethnic Russians, and the possibility that NATO troops will be stationed at its border.
NATO Secretary General Jaap de Hoop Scheffer said that air defence patrols over the Baltic states could start straight away.
Russia fears these patrols could be used to spy on its territory.
Mr De Hoop Scheffer, who will go to Moscow in early April, acknowledged there could be problems with Russia over the Conventional Forces in Europe treaty which limits troop numbers in eastern Europe.
