NATO said on Thursday that it still sees no drawdown of Russian troops from near the Ukrainian border, two days after Moscow announced it would reduce its presence there, raising hopes of detente in a tense situation.

"There are signs from Moscow that diplomacy could continue, but so far we have not seen any sign of withdrawal or de-escalation," NATO Secretary-General Jens Stoltenberg said at defense ministers' talks in Brussels.

British Defense Secretary Ben Wallace said that nearly 60% of Russia's land combat forces were now concentrated near the Ukrainian borders, 150,000 or more in real terms. Russia has been amassing soldiers and equipment there for several months, prompting fears in Kyiv and other Western capitals that plans for an invasion could be afoot.

Wallace's comments came after a high-ranking White House official said that despite Moscow's claims to the contrary, it was still sending troops to the border – perhaps as many as 7,000 troops in recent days.

European Union leaders are to discuss the crisis on the sidelines of a Brussels summit on Thursday.

Russia annexed the Ukrainian peninsula of Crimea in 2014, and has also been backing pro-Russian separatists in its neighbour's eastern Donbass region who are battling Ukrainian government forces. The latter get backing from NATO countries.

Kremlin spokesperson Dmitry Peskov said Moscow would respond on Thursday to a letter sent by the United States on a set of Russian security demands made in the current crisis. These include that Ukraine never join NATO and that the alliance pull back troops stationed in eastern Europe since 2014.