As the Ukraine crisis continues, NATO says it will take whatever steps are necessary to increase the security of its allies.
It claims it has seen no sign of Russian troops withdrawing from the Ukrainian border.
Arriving in Estonia for a two-day visit, NATO Secretary-General Anders Fogh Rasmussen said that defence plans could be revised.
“We are now considering further steps to further re-enforce our collective defence and those further steps might include updated defence plans, new defence plans, enhanced exercises and also appropriate deployments,” he said.
NATO has been massing its troops in southern Poland – with American, Canadian and Polish paratroopers taking part in exercises.
The alliance accuses Moscow of using special forces in the separatist takeover of mainly Russian-speaking eastern Ukraine.