Jens Stoltenberg, the NATO secretary-general, said alliance defense ministers will formally approve the deployment plan drafted by NATO military planners at a meeting that begins Tuesday in Brussels.

Estonia, Latvia, Lithuania and Poland, four of NATO's members that feel most threatened by Russia, will each be reinforced by "a robust multinational battalion," Stoltenberg told a news conference.

"This will send a clear signal that NATO stands ready to defend any ally," the alliance chief said.

There was no immediate reaction from Moscow. The Kremlin has accused NATO of moving more and more military forces close to its borders, and vowed to do what it takes to protect Russia's national security and interests.