NATO's chief says the alliance will agree this week to send four multinational battalions to the Baltic states and Poland to boost their defenses against Russia.

Jens Stoltenberg, the NATO secretary-general, said Monday that alliance defense ministers will formally approve the deployment plan 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.

NATO officials have said the alliance units will be rotated in and out of the host countries, rather than being based there permanently.