The decision by the upper house of parliament takes immediate effect - and it could presage a broader attack on Ukraine.

On Monday, Moscow recognised the independence of Russian-backed rebel regions in eastern Ukraine.

Some Western leaders have said Russian troops had moved into Ukraine's east - and the US called it an "invasion".

In Brussels NATO Secretary-General Jens Stoltenberg said Russia is planning for a "full-scale" attack on its neighbour.

"Every indication is that Russia is continuing to plan for a full-scale attack of Ukraine," he told a news conference.