Hours after arriving in the Netherlands for a nuclear summit, Obama held one-on-one talks with Chinese President Xi Jinping. China has often sided with Russia in disputes with the West, but U.S. officials have been appealing to Beijing's well-known opposition to outside interference in other nation's domestic affairs.
Obama treaded carefully in statements with Xi before their meeting, saying only that they planned to discuss the situation in Ukraine.
"I believe ultimately, that by working together, China and the United States can help strengthen international law and respect for the sovereignty of nations and establish the kind of rules internationally that allow all peoples to thrive," Obama said in a subtle appeal for Chinese support.
He added that he and the Chinese leader would also seek to "work through frictions that exist in our relations" on matters like human rights and maritime disputes.
Xi, for his part, pointed to areas of potential cooperation with the U.S. as he settled in for what Obama described as a wide-ranging session. "It is like a menu - and a rich one at that," Xi said through an interpreter.
Obama's meeting with Xi opened a week of international travel where crisis in Ukraine tops the agenda. After arriving in the Netherlands on a sunny and brisk Monday morning and meeting with Dutch Prime Minister Mark Rutte, Obama asserted that the U.S. and Europe stand together behind Ukraine.
No issue commands more of Obama's and Europe's attention than Russia's annexation of the Crimean Peninsula and the fear that Moscow could decide to expand further into Ukraine. But Obama also is attempting to use his weeklong trip to personally reconnect not only with Europe but Asia and the Middle East, all strategically crucial regions with their own tensions and qualms about the U.S.
Obama's meeting with Xi highlighted another tricky front in U.S. international relations and comes just a day after The New York Times and the German magazine Der Spiegel reported that the U.S. National Security Agency had hacked into the servers of Chinese telecommunications giant Huawei.
Meanwhile, China has been wary of Obama's efforts to increase U.S. influence in the Asia Pacific region. The U.S. has also called for restraint in China's maritime territorial disputes with Japan and its Southeast Asian neighbors.
China, a frequent Russian ally, abstained a week ago from voting on a United Nations Security Council resolution declaring Crimea's secession referendum illegal. With Russia vetoing the measure and the 13 other council members voting in favor, China's abstention served to isolate Moscow internationally.
Nuclear terrorism was the official topic as Obama and other world leaders streamed in to a convention center in The Hague for a two-day nuclear summit. It opened Monday with Japan announcing it would turn over to the U.S. more than 700 pounds of weapons-grade plutonium and a supply of highly-enriched uranium, a victory for Obama's efforts to secure nuclear materials around the world.
But the headline event of the day is a Ukraine-focused, hurriedly scheduled meeting of the Group of Seven industrialized economies - the U.S., Britain, Canada, France, Germany, Italy and Japan.
On Tuesday, Obama plans a joint meeting with Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye, a session preceded by a sit-down with Prince Mohamed bin Zayed, crown prince of Abu Dhabi, the richest emirate in the United Arab Emirates federation.
In an interview with the Dutch newspaper de Volkskrant published before he arrived Monday, Obama says his message to European leaders is that Russian President Vladimir Putin needs to "understand the economic and political consequences of his actions in Ukraine."
Still, he said he does not view Europe as a battleground between the East and the West. "That's the kind of thinking that should have ended with the Cold War," he said. "On the contrary, it's important that Ukraine have good relations with the United States, Russia, and Europe."
Discussion among Obama and his G-7 counterparts will center on economic aid to Ukraine, while at the same time seeking to segregate Putin from the exclusive group, which Russia usually joins in Group of Eight meetings.
More broadly, the Ukraine crisis will test Obama's ability to forge a unified and forceful stance against Russia from European leaders who are alarmed by Putin's moves but whose economies are dependent on Russian energy and trade.
In the interview, Obama conceded that the sanctions he has threatened against Russian economic sectors could have worldwide impacts.
But, he added: "If Russia continues to escalate the situation, we need to be prepared to impose a greater cost."