The president reassured his Polish hosts that despite Russia's objections, the U.S. will base fighter jets in Poland, and will go ahead with its planned missile defense system.

“We believe that missile defense is something where we should be cooperating with the Russians, because we share external threats, and this would not be a threat to the strategic balance that Russia is concerned with,” he said.

Warsaw was the final stop in Obama's six-day trip to Europe. In Poland, as in Ireland, Britain and France, the president emphasized the importance of U.S.-European relations. “It is fitting that I conclude my trip here in Poland. At each stop I have affirmed the fact that America's transatlantic alliance is the cornerstone of our engagement in the world,” he said.

Obama concluded his European tour by paying respects at a memorial to the late Polish President Lech Kaczynski and 95 others, many of them top government officials, who died in a plane crash in April 2010.