NATO would station 4,000 troops in Poland and the Baltic States, the Wall Street Journal reported on Friday. The United States is likely to provide two battalions, Germany and Britain one each.

U.S. Deputy Secretary of Defense Robert Work, visiting Brussels, confirmed the overall size of the force and said the buildup was a response to more Russian activity around the Baltics where tensions have been rising.

"The Russians have been doing a lot of snap exercises right up against the borders, with a lot of troops," Work said in an interview. "From our perspective, we could argue this is extraordinarily provocative behavior."

Russian officials have repeatedly said their own buildup and exercises are a response to NATO's troop buildup and aggressive posture to Moscow.

NATO defense ministers in February approved in principle the deployment of an Eastern European troop presence, though diplomats said the new numbers weren't final.

The force is intended to be multinational, and NATO is asking smaller members to make a contribution for in the form of logistics and support forces.

Of special importance is the participation of a sizable German force. German officials said Friday that they were considering plans ahead of NATO’s Warsaw summit in July this year for a battalion to be based in Lithuania, but a final decision hadn't been reached.

Before the deployments are completed, one point of contention could be whether the infantry forces within each battalion should be from one nation or many. Some NATO officials believe each battalion should be from a single country, to ensure it can fight effectively.

But U.S. and NATO officials have said that to make sure the force was a real deterrent to Russian aggression they would like it to operate under the alliance's flag as well as command and control system.

The alliance is still determined to follow the conditions of the 1997 NATO-Russian Founding Act, which prohibits permanently stationed troops in large numbers along the Russian border. While the Founding Act does not specify an exact number of troops, NATO officials believe four battalions are within the limits of the agreement.

Andres Sang, spokesman for the Estonian Defense Ministry, told Postimees that was still too early to say at this point how many extra soldiers would be stationed in the region, and in which country.