"I want to thank Greek people for their humanitarian response" and their "extraordinary compassion," Obama said in Athens as he began a final foreign trip to Europe.

Over a million people passed through Greece last year, and the crisis-hit country has struggled to accommmodate over 60,000 refugees left stranded on its territory when Balkan states farther north shuttered their borders earlier this year.

Even with EU funds and assistance, there is overcrowding in Greek camps and frequent brawls between rival ethnic groups.