Washington (AFP) - US President Barack Obama headed across the Atlantic late Monday on his final foreign trip while in office -- a farewell tour of Europe and a summit with Asia-Pacific leaders to reassure concerned allies after Donald Trump's election.
Obama will first go to Greece, his first trip to the birthplace of democracy, where he will visit the Parthenon and hold talks with the country's leaders.
Security will be tight in central Athens, with thousands of police officers on the streets and traffic cut off for several hours.
Civil servants, communists, far-left groups and anarchists all plan to hold demonstrations as Obama swings through the Greek capital.
He then heads to Germany for key discussions with German Chancellor Angela Merkel, long one of his closest foreign partners.
He will also meet there with French President Francois Hollande, British Prime Minister Theresa May and Italian Prime Minister Matteo Renzi.
The leaders plan to discuss the crises in Syria and Ukraine, as well as the fight against the Islamic State group.
In a pre-trip news conference, Obama told reporters he would "signal our solidarity with our closest allies and express our support for a strong, integrated and united Europe."
"It's essential to our national security and it's essential to global stability," he said.
"That's why the trans-Atlantic alliance and the NATO alliance have endured for decades under Democratic and Republican administrations," he added, seeking to allay fears that Trump will seek to sideline the alliance.
Obama also said he believes his successor has a "commitment to NATO."
The American president will conclude his trip with a stop in Peru for a summit of the Asia-Pacific Economic Cooperation forum (APEC). Among the leaders he is expected to meet there is President Xi Jinping of China.
"This is a time of great change in the world, but America's always been a pillar of strength and a beacon of hope to peoples around the globe. And that's what it must continue to be," Obama said.