Russia's defense ministry said on Sunday that it is complying with international troop limits near its border with Ukraine, after NATO's top military commander voiced concern over the size of Russian forces near the border.

"The Russian Defense Ministry is in compliance with all international agreements limiting the number of troops in the border areas with Ukraine," Russian Deputy Defense Minister Anatoly Antonov was quoted by Russian news agencies as saying.

NATO's Supreme Allied Commander Europe, US air force General Philip Breedlove, said on Sunday that the Russian force near its Ukrainian border was "very, very sizeable and very, very ready".

He said he was worried it could pose a threat to Moldova's mainly Russian-speaking separatist Transdniestria region.

Russia launched a military exercise involving 8,500 artillery soldiers near Ukraine's border 10 days ago.

On Sunday, Russian forces consolidated control over Crimea, two days after President Vladimir Putin signed laws completing Russia's annexation of the Black Sea peninsula. The Russian Defense Ministry said on Sunday that the Russian flag had been raised over 189 Ukrainian military installations in Crimea.

With Russia's military on the move, some have voiced fears Putin may try to grab more territory in the east of Ukraine.

However, Antonov said eight groups of international inspectors had conducted missions in Russia in the last month to check on Russian troop movements.