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STORY: Sweden and Finland were both neutral throughout the Cold War, and their decision to join NATO is one of the most significant changes in Europe's security architecture for decades, reflecting a sweeping shift in public opinion in the Nordic region since Russia's Feb. 24 invasion.

"The applications you have made today are a historic step. (NATO) allies will now consider the next steps on the path to NATO. The security interests of all allies have to be taken into account, and we are determined to work through all issues and reach rapid conclusion," NATO Secretary-General Jens Stoltenberg said at a short ceremony in which the Swedish and Finnish ambassadors to the alliance handed over their application letters, each in a white folder embossed with their national flag.

Ratification of all 30 allied parliaments could take up to a year, diplomats say.

Turkey has surprised its allies in recent days by saying it had reservations about Finnish and Swedish membership.