Asian markets fell and oil prices rose Thursday on growing fears of a war in eastern Europe after Moscow said separatists had called for help to repel Ukrainian forces and Vladimir Putin announced a  military operation.

US officials had warned of an imminent incursion by Russia after the Kremlin this week recognised two breakaway regions in Ukraine and said it would provide "peacekeepers".

Russian President Putin is said to have around 200,000 soldiers amassed on the border with Ukraine, borders and Washington said many are in attack positions.

World leaders continue to work for a de-escalation but have so far failed, while Ukrainian President Volodymyr Zelensky said he had tried to call Putin but there was "no answer, only silence".

He added that Russia could start "a major war in Europe" in the coming days.

And the United Nations was told a full-scale Russian invasion would have a devastating global impact that would likely spark a new "refugee crisis".

The threat of a conflagration has sent markets spiraling, with traders fretting over supplies of key commodities including wheat and metals.

Crucially, oil has soared to within spitting distance of $100, and both main contracts were up more than one percent Thursday.

"Russia/Ukraine tensions bring both a possible demand shock (for Europe), and more importantly a much larger supply shock for the rest of the world given the importance of Russia and Ukraine to energy, hard commodities and soft commodities," said National Australia Bank s Tapas Strickland.

The crisis comes as governments struggle to contain runaway inflation fueled by demand as life returns after recent lockdowns, with many fearing the fragile global economic recovery from the pandemic could be knocked off course.

After staging a slight bounce Wednesday in reaction to what were considered light sanctions against Moscow, Asian markets were back in the red after a hefty drop on Wall Street.

Hong Kong, Tokyo, Shanghai, Seoul, Sydney, Singapore, Taipei, Jakarta and Wellington all fell.