NATO and the United States are switching their defence doctrine from assurance to deterrence in Eastern Europe in response to a "resurgent and aggressive Russia", the top US general in Europe said Thursday.

The comments by General Philip Breedlove in the Latvian capital Riga come a day after the Pentagon said it would begin continuous rotations of an additional armoured brigade of about 4,200 troops in Eastern Europe beginning in early 2017.

"We are prepared to fight and win if we have to... our focus will expand from assurance to deterrence, including measures that vastly improve our overall readiness," Breedlove said following talks with Baltic region NATO commanders.

"To the east and north we face a resurgent and aggressive Russia, and as we have continued to witness these last two years, Russia continues to seek to extend its influence on its periphery and beyond."

Russia annexed Crimea in 2014 and has been supporting a pro-Moscow separatist conflict in eastern Ukraine.

Eastern NATO members including the formerly Soviet-ruled Baltic states and Poland have since lobbied the alliance to increase its presence in the region.

"In the spring of 2017 what we will bring to Europe, and then again put into the three Baltic nations, is an armoured brigade fully enabled with command and control and all of the supporting equipment required," Breedlove said.

Asked by AFP whether he expected other NATO members to match the upped US troop commitment, Breedlove said: "We would hope (so)."

"What we have seen is that when we led by coming here with company-sized formations after (Russia's actions in) Crimea and Donbas, other nations have shown up now with company-sized formations."

Russia has repeatedly warned against the permanent positioning of substantial forces from NATO along its border.

And some NATO members, like Germany, have been sceptical about any substantial permanent deployment, saying it could breach a 1997 agreement between the military alliance and Russia.

But the new US deployment avoids the issue because it is not technically permanently stationed in Eastern Europe, with brigades rotating in and out, US officials say.