NATO Secretary-General Jens Stoltenberg says Russia is taking military action against Ukraine and has condemned Moscow’s decision to recognize separatist areas of southeast Ukraine as independent.

Stoltenberg called the move Tuesday a “serious escalation by Russia and a flagrant violation of international law.” The NATO chief called the military action a “further invasion" of Ukraine by Russia which had already invaded its neighbor in 2014.

He added that there’s “every indication” Russia continues to plan for a full-scale attack on Ukraine.

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

He said that the NATO response force remains on high readiness but is not yet being deployed, although some allies are moving troops, ships and planes into the Baltic states and near the Black Sea to defend other NATO members.