NATO is to send four multi-national battalions to the Baltic states and Poland in a bid to boost its defences against Russia.
Secretary general Jens Stoltenberg said that alliance defence ministers will formally approve the deployment plan at a meeting that begins on 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", Mr 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.
US Nato ambassador Douglas Lute said details of the number of troops to be deployed as well as the national composition of the battalions and who will be in their command will be decided and announced at the July Nato summit in Warsaw.
Nato officials say that some 4,000 troops will be involved.
Mr Lute said the rotation will be on the heel-to-toe basis, meaning the troops will be present in the host countries every day of the year.
Mr Lute said the troops will remain as long as is necessary.
The United States, Britain and Germany have already committed to acting as so-called framework nations for three of the battalions.
It was not immediately clear which Nato member country would agree to furnish the core forces for the fourth battalion.
