Obama and Xi spoke yesterday, their first known conversation since Russian forces took control of Crimea.
Chinese officials, who often side with Russia against the West, have been cautious in their public comments thus far.
The White House, in a readout of Obama and Xi's call, said the two leaders "agreed on the importance of upholding principles of sovereignty and territorial integrity, both in the context of Ukraine and also for the broader functioning of the international system."
Obama's call to Xi was part of a broader effort by the president to rally world leaders around the notion that Russia's incursion into Crimea violates international law.
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Ahead of that vote, Obama will host Ukrainian Prime Minister Arseniy Yatsenyuk at the White House on Wednesday. The US has promised Ukraine's new government USD 1 billion in loan guarantees, which would supplement a USD 15 billion aid pledge from the European Union.
In wooing China's support, the US is seeking to capitalise on Beijing's policy of non-interference. US officials say China may also be viewing the situation in Crimea through the prism of its own ethnic minorities in border regions.
Russia moved into Crimea after Ukraine's pro-Kremlin President Viktor Yanukovych fled the capital of Kiev. Yanukovych had faced three months of political protests after he scrapped plans to strengthen ties with Europe, a move Russia opposed.