NATO Secretary-General Jens Stoltenberg has said that Russia is taking military action against Ukraine and condemned Moscow's decision to recognize the independence of the Donetsk and Luhansk people's republics, AP reported.

Stoltenberg called the move "a serious escalation by Russia and a flagrant violation of international law".

The NATO chief also described the military action as a "further invasion" of Ukraine by Russia, "which has already invaded its neighbour's territory in 2014".

He added that there was "every indication" that Russia was continuing to plan a full-scale attack on Ukraine.

Stoltenberg said NATO allies have more than 100 military aircraft on high alert and more than 120 warships at sea from the Arctic Circle to the Mediterranean Sea.

He said the NATO Response Force remains on high alert but not yet deployed, although some Allies are moving troops, ships and aircraft to the Baltic states and near the Black Sea to protect other NATO members.