WASHINGTON, June 2 -- President Barack Obama on Monday evening embarked on a four-day tour of Poland, Belgium and France to reassure U.S. commitment to the security of its allies in the light of the ongoing Ukrainian crisis.

While in Warsaw, Poland's capital, Obama is scheduled to meet with leaders of the Central and Eastern European nations on Tuesday and Ukraine's President-elect Petro Poroshenko on Wednesday. He will also make a speech on U.S.-European relations.

The president will "have a chance to reaffirm America's unwavering commitment to secure democracy and to the security of our Eastern European allies," Benjamin Rhodes, Obama's deputy national security adviser, told reporters.

In Brussels, Obama will have a summit with the leaders of six other industrialized nations -- Britain, Canada, France, Germany, Italy and Japan, with focus on Ukraine and other foreign policy issues.

The annual event was originally slated for early June in Sochi, Russia, but Moscow was suspended from the gathering and the venue was changed to Brussels following the Russian annexation of Crimea from Ukraine in March.

Obama will be in Normandy, France on Friday for events marking the 70th anniversary of D-Day, where he will be joined by other leaders including Russian President Vladimir Putin.

Rhodes said there will be no bilateral meeting between the two leaders, but he did not rule out an informal interaction as they are "in the same place."