NATO warned on Wednesday that Russia's military presence on the flashpoint border with Ukraine was of "grave concern" and that Moscow's forces could reach military objectives in just days.

Russian troops are poised to attack within 12 hours and could invade vast portions of Ukrainian territory in three to five days, General Philip Breedlove, NATO's top commander, told two American newspapers.

NATO Secretary General Anders Fogh Rasmussen said he shared that assessment and warned of a "very massive Russian military buildup along the Ukrainian border" which NATO estimates at about 40,000 troops.

"This is really a matter of grave concern," Rasmussen said, at the close of a NATO foreign ministers' meeting in Brussels.

Breedlove told The Wall Street Journal potential targets for Russia included a land corridor linking Crimea and mainland Russia, the taking of the strategic Odessa port or an occupation of the breakaway Russian-speaking region of Transdniestr in Moldova.

"They are absolutely able to bring great force to a position of readiness," he told The New York Times.

"That is something that we have to think about: what does that mean geostrategically that we now have a nation that can produce this ready force and now has demonstrated that it will use that ready force to go across a sovereign boundary?"

He said the Russian troop deployments may be meant as a "coercive force" in talks with the West over the Ukraine crisis and ahead of a Ukrainian presidential election next month.

Rasmussen warned that if Russia were to intervene further in Ukraine, he "would not hesitate to call it an historic mistake".

"It would be a miscalculation with huge strategic implications," he said.

The warning came the day after NATO announced the alliance was suspending all practical cooperation with Russia, military and civilian, and that there was no confirmation that Russian troops were pulling back from the border.

burs-jhb/mdl

New York Times