Germany, Britain, the United States and Canada currently lead four multi-national "battlegroups" in Estonia, Latvia, Lithuania and Poland, as tripwires against possible Russian adventurism.
"Today, we declare that (these battalions) are ready and able to deter and, if necessary, immediately respond to any aggression in concert with national forces underpinned by a viable reinforcement strategy," the defence ministers said in a joint statement at a Brussels summit.
Under a programme called the Enhanced Forward Presence (EFP), NATO deployed the battalions in Poland and the Baltic states, a region formerly under Moscow's control, following alarm over Russian actions in Ukraine and Syria.
Adding to tensions, Russia is preparing massive military exercises in its west in September, and has deployed a missile system in the neighbouring enclave of Kaliningrad.
NATO agreed at a 2016 summit in Warsaw to boost NATO's military presence along the alliance's eastern flank.
The four battalions, which deploy on a rotational basis, total about 4 500 troops from 15 member nations and train constantly to improve co-ordination and conduct joint exercises.
The EFP "is a direct response to Russia's aggressive actions, including provocative military activities in the periphery of NATO territory, which have reduced stability and security, increased unpredictability, and changed the security environment," the joint declaration said.