Within minutes of stepping on Polish soil, Obama will meet US and Polish F-16 fighter pilots who are mounting joint patrols that were stepped up after the Russian annexation of Ukraine's Crimea peninsula in a symbolic signal to Moscow of US intent.

He will also use an overnight stay in Warsaw to meet Ukraine's president-elect Petro Poroshenko on Wednesday, in a sign of support for the newly elected leader's bid to tilt the country West after his solid election win and navigate out of an economic and political crisis.

The White House also announced on Monday that Vice President Joe Biden will travel to Kiev on Saturday to attend Poroshenko's inauguration underscoring US position that the people of Ukraine and not Moscow should decide their destiny.

Obama's tour later takes in the Group of Seven summit in Brussels, which will be dominated by a US push to sometimes reluctant Europe to maintain the economic pressure on Russia.

The summit will take place in the shadow of a major offensive by hundreds of pro-Russian gunmen who struck a Ukrainian border guard camp with mortar and grenade fire on Monday, in an expanding insurgency which Washington says is directed by Moscow.

Obama will also visit France, for talks with President Francois Hollande in Paris and will attend 70th anniversary commemorations of the D-Day Normandy landings to complete his second trip to Europe this year.

In Normandy, Obama will come face-to-face with Russian President Vladimir Putin, in a potentially prickly encounter, given that US leader has spent months trying to isolate his rival and punish the Kremlin inner circle with sanctions over Ukraine.

The White House says there will be no one-on-one meeting between Obama and Putin on the sidelines of several events featuring heads of states and leaders attending the World War II commemoration.

But senior aides have not ruled out an informal encounter which would be the first for the rivals since the Ukraine crisis mushroomed into the worst East-West standoff since the Cold War earlier this year.


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