NATO chief Jens Stoltenberg on Wednesday demanded that Russia withdraw its forces and military hardware from Ukraine and halt its support for pro-Moscow separatists battling Kiev.

NATO chief Jens Stoltenberg on Wednesday demanded that Russia withdraw its forces and military hardware from Ukraine and halt its support for pro-Moscow separatists battling Kiev.

"Russia needs to stop supporting the militants and withdraw its forces and military equipment from Ukrainian territory," Stoltenberg said after a meeting of NATO defense ministers with their Ukrainian counterpart in Brussels.

He said the US-led alliance will continue to stand by the government in Kiev and would never recognize Russia's "illegal and illegitimate annexation of Crimea".

"In response to Russia's actions, NATO has stepped up its support for Ukraine. Our level of political and practical engagement since 2014 is unprecedented," he said.

Stoltenberg said Moscow continued to support the rebels in many ways, supplying equipment and advisors while it massed troops along the border with Ukraine and built up its military presence in Crimea, home base for its key Black Sea fleet.