PARIS (AFP) - China's support for Russia in the standoff over Ukraine upends the strategic calculus for US President Joe Biden, who must now contend with a second front in a geopolitical fight whose ramifications could be felt worldwide.

By criticising on Friday (Feb 4) Washington's alleged destabilising policies in both Eastern Europe and the Asia-Pacific region, Beijing and Moscow indicated that sanctions alone would not deter their bids to play larger roles on the global stage.

Appearing publicly as the Beijing Olympics opened, Russian President Vladimir Putin and his Chinese counterpart Xi Jinping showed an "enhanced commitment to make the world safe for authoritarianism, in particular in former socialist countries," said Steve Tsang, a political scientist at the SOAS University of London.

And for Xi, taking a public stand on Ukraine demonstrates "his shared interest with Putin to challenge the US-dominated world order", Tsang told AFP.

Official Chinese media outlets have been playing up the frequent encounters between Xi and Putin since Russia's 2014 annexation of Crimea, which saw the Russian leader largely blacklisted by the West.

China's Global Times noted recently that "besides the official meetings, the two also shared some close moments like enjoying vodka, caviar and Russian ice cream and celebrating each other's birthdays".

"We know that both Russia and China value sovereignty above anything else, so alliance is still too strong of a word," said Anton Barbashin, an analyst at the Riddle think-tank in Glasgow, Scotland.

"But we are definitely going to see more coordinated action in international relations, maybe simultaneous campaigns in Europe and Asia, as well as deepening economic ties between Moscow and Beijing," he told AFP.

'Opportunity costs'

And the Ukraine crisis gives Xi a chance to riposte indirectly to Biden's avowed focus of containing China's ambitions in the Asia-Pacific, as evidenced by the recent US-Australia defence pact and nuclear submarines deal.

"It increases Russia's relative importance for China - Xi couldn't have provoked Biden nor Europe this openly," said Pascal Ausseur, a former French navy admiral and director of the Mediterranean Foundation of Strategic Studies.

"And Putin showed Xi that he knows how to take geopolitical and military risks, which Beijing must have appreciated," he said.

Putin is using the threat to invade Ukraine to demand a halt to Nato expansion and what Mosow calls "Cold War" ideologies, and now has Beijing's explicit support in the showdown.

"Don't forget that Barack Obama told Putin that Russia was only a regional power - he wants to show that Russia plays a central role, and he's succeeding," Ausseur said.

The payoff for China, meanwhile, could be in its own backyard: More US troops focusing on Ukraine and other Eastern European nations means less military weight to compete with Beijing in the Pacific.

The US response to Moscow on any Ukraine invasion, for example, could weigh heavily on any Chinese move to take control of Taiwan. Washington helps provide Taiwan with the means to defend itself under the US Taiwan Relations Act, but does not explicitly promise to come to the island's help in the event of war.

"US strategies designed to deter or overextend Russia should not inadvertently overextend the United States by imposing high opportunity costs," RAND Corp analyst Stephanie Pezard wrote in a recent analysis.

Both Russia and China would also seize on any apparent US backdown over Ukraine to portray Washington as an unreliable partner, a potent argument as both countries look to spread their global influence, in particular in Africa.

"If the United States chooses retrenchment rather than its traditional global leadership role, both Russia and China could try to fill the void," Pezard said.

Experts also agreed that time is on Putin's side, as he left Moscow to meet with Xi in Beijing ahead of the opening of the of the Winter Olympic Games - which Biden and other Western leaders pointedly snubbed.

"Putin should be able to get Xi to commit to support Russia should the Ukraine situation end up with Russia being sanctioned - but probably on the understanding that Putin will not spoil Xi's Winter Games" by invading Ukraine during the competitions, Tsang said.