NATO Secretary-General Jens Stoltenberg says the military alliance will agree this week to send four multinational battalions to Poland and the Baltic states to boost their defense and show that NATO is "ready to defend any ally."

Stoltenberg said on June 13 the new plans are due to be formally approved at a NATO defense ministers' meeting that begins in Brussels on June 14.

"NATO has taken robust action to protect our nations and to contribute to stability in our neighborhood," Stoltenberg said. "But the challenges we face are enduring, so we need to be prepared for the long haul."

Stoltenberg said the battalions will be deployed on a rotational basis rather than being based permanently in countries.

The easternmost of NATO's 28 members, Estonia, Latvia, Lithuania, and Poland have said they feel threatened by Russia in light of its illegal annexation of Ukraine's Crimean Peninsula and support for separatists in eastern Ukraine.

U.S. NATO Ambassador Douglas Lute said details of the number of troops to be deployed and from which countries will be announced at the July NATO summit in Warsaw.

NATO officials say some 4,000 troops will be involved in the new deployments.

The United States, Britain, and Germany have committed to acting as so-called framework countries for three of the battalions.

Based on reporting by AP and dpa