Warsaw, AP—President Barack Obama conferred Wednesday with Ukraine’s future leader amid hopes he could guide the nation out of crisis, as Western leaders who had united against Russia diverged on their diplomatic approach.

Obama’s meeting with Petro Poroshenko in Warsaw came 10 days after the billionaire candy maker was chosen as Ukraine’s first elected leader since its pro-Russian president fled and Moscow annexed the Crimean Peninsula in a confrontation that has reignited old global divisions.

US Secretary of State John Kerry met with Poroshenko ahead of the president at the Marriott Hotel where the American delegation in Warsaw was staying, and said the United States looked forward to celebrating Poroshenko’s inauguration on Saturday.

“He won everywhere, and clearly has been given a mandate to try to lead the country into a new era,” Kerry said. Poroshenko thanked the American people for supporting democracy and freedom in Ukraine.

Obama was in Warsaw to help commemorate the 25th anniversary of Poland’s first partially free election, an example of democratic progress that the US president plans to point to in a speech Wednesday as a model for Ukraine.

“What we have learned from our history—and nobody understands that better than the Poles—is that basic principles of territorial integrity and sovereignty and freedom, the ability for people to make their own determinations about their country’s future, is the cornerstone of the peace and security that we’ve seen in Europe over the last several decades,” Obama said in a news conference on Tuesday.

“That is threatened by Russian actions in Crimea, and now Russian activity in eastern Ukraine,” the president added.

Obama warned Russian President Vladimir Putin not to stoke divisions in Ukraine and instead to recognize Poroshenko’s election and begin rebuilding trust with the West.

World leaders excluded Putin from a G7 meeting starting Wednesday night in Brussels that was originally slated to include Putin and take place in Sochi, Russia. But in recent days, the leaders of Britain, France and Germany have scheduled face-to-face talks with the Russian leader, exposing divisions among Western nations that had united to isolate Russia over its aggressive moves against Ukraine.

Obama and Putin have spoken by phone multiple times—but not in person—since Russia annexed Crimea and stationed tens of thousands of troops on its border with Ukraine. Obama said Tuesday he maintains a “businesslike relationship” with Putin and is certain to encounter him in France on Friday during events to commemorate the 70th anniversary of the Allied invasion of Normandy. But they have no formal talks scheduled.

“If, in fact, we can see some responsible behavior by the Russians over the next several months, then I think it is possible for us to try to rebuild some of the trust that’s been shattered during this past year,” Obama said. “But I think it is fair to say that rebuilding that trust will take quite some time.”

Obama said contingencies for dealing with future destabilization by Putin include further sanctions against Russia. Upon arrival in Warsaw, Tuesday, he also announced a plan to beef up the US military presence in the region. He proposed up to 1 billion US dollars to boost deployments and exercises throughout Europe, a significant departure from a two-decade trend toward a smaller US military presence on the continent.

The White House is casting Obama’s speech at the Freedom Day celebration on Wednesday in Royal Castle Square as the centerpiece of his three-country European tour, a unique opportunity to make the case directly in the region for Ukraine’s solidarity. Obama told NATO allies on Tuesday that citizens across central and eastern Europe must know that “no other nation can take away” what they’ve built in the 25 years since the dissolution of the Soviet Union.

“The president-elect of Ukraine has indicated his willingness to work with all regions of Ukraine to create a constitutional order that is representative of all people. And he has said that he is interested in pursuing good relations with Russia.” Obama said at a Polish Solidarity Dinner with Poroshenko on Wednesday. “But what he has said, and he is right to say, is that the sovereignty of Ukraine should not be sacrificed in that effort, and we fully support him in that.”