Visiting Jordan Friday, President Obama and King Abdullah discussed Syria.
Mr. Obama pledged $200 million in U.S. aid for Syrian refugees arriving in Jordan.
The president also commented on the Israeli-Palestinian conflict.
"We're just going to keep on plugging away," Mr. Obama said. "The window of opportunity still exists but it's getting more and more difficult."
Earlier Mr. Obama met Palestinian leader Abbas in Bethlehem, at the Church of the Nativity.
In Jerusalem he paid a visit to Yad Vashem, the Holocaust memorial.
He visited the grave of Theodore Hertzl, father of Zionism, and placed a stone from the Martin Luther Memorial on the grave of Israeli Prime Minister Rabin, assassinated for trying to make peace with Palestinians.
Many Israelis were moved by the visit, but will Israel join the president's call for peace talks?
"Trust us, we need to decide which road do we go and not the Americans, not Obama," said one Tel Aviv resident.
Still, the trip could build Israeli trust in the U.S. President.
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