The two heads of state discussed security as they observed a military exercise in the Suwalki Gap, a corridor that runs the length of the Polish-Lithuanian border, between Russia's heavily militarised Kaliningrad exclave and Belarus.

"The idea of deploying nuclear weapons is not warmongering or threatening Russia. It's an element of the deterrence system, which should act as a really significant deterrent factor," Lithuanian President Gitanas Nauseda told reporters.

Polish President Andrzej Duda has in recent days proposed stationing nuclear weapons in Poland, though the idea has been dismissed by others in Poland, including Prime Minister Donald Tusk.

On Friday, Duda again brought up the idea.

"The whole NATO territory, in our understanding, must be defended appropriately, adequately, so it is very logical that a nuclear system should be relocated to NATO's eastern flank," he said.

"We, as one of these countries, have declared our readiness to host this weapon," he added.

The presidents spoke during the Brave Griffin 24/II military exercise in the Alytus district of Lithuania.

During the exercise, 1,500 troops tested defence scenarios in the Suwalki Gap, considered the Achilles' heel of NATO's eastern flank.