Barack Obama arrived in Jordan yesterday to face scrutiny over his Syria strategy, on the last leg of a Middle East tour after challenging Israelis to embrace peace with Palestinians.
The presidential aircraft landed at Queen Alia Airport near Amman and Obama was welcomed by Jordanian Foreign Minister Nasser Judeh and other senior officials.
He headed to the royal palace for talks and a private dinner with King Abdullah II, a key US ally, on the agony of Syria's conflict in Jordan, which hosts more than 450,000 refugees from the war-torn country.
Obama will also support political reform efforts inside Jordan, which has been an oasis of relative calm in a region swept by turmoil of the Arab Spring.
The US leader wrapped up a three-day trip to Israel and the Palestinian territories, his first as president, with a visit to Bethlehem's Church of the Nativity.
While the thrust of his Israel trip was reassurance Washington would mount an "eternal" defence of the Jewish state in the face of the Iranian nuclear threat, Obama is to focus on the Syria conflict on his stop in Amman.
The number of Syrian refugees is expected to rise to 700,000 by the end of this year, as people fleeing the vicious fighting between Bashar al-Assad's forces and rebels spill over its borders.
Obama has resisted pouring US arms or ammunition into the conflict, which the UN estimates has cost at least 70,000 lives, but has offered logistical support to rebels and hundreds of millions of dollars in humanitarian aid.
A senior US official said Obama wanted to coordinate with the king on security challenges and on helping Jordan alleviate the refugee crisis.
"We're also working very closely with the Jordanian government as part of the coalition of countries that is supporting the Syrian opposition to pressure the regime, to build up the opposition, and try to bring about a new Syria," the official added.
In Jerusalem, Obama said the United States was investigating claims chemical weapons had been used in Syria, warning it would be a "game-changer" and that Assad's regime would he held accountable.
Yesterday morning, Obama visited the grave of Theodor Herzl, the father of modern Zionism, then paid his respects at the grave of murdered Israeli premier Yitzhak Rabin, where he placed a stone from the grounds of Washington's Martin Luther King memorial.
He also toured Yad Vashem Holocaust Museum, saying it showed "the barbarism that unfolds when we begin to see our fellow human beings as somehow less than us".
After a brief meeting with Israeli prime minister Benjamin Netanyahu, Obama set off for Bethlehem, travelling by motorcade, not helicopter, after a sudden sandstorm swept the city.
The change of plan gave Obama an unscheduled experience of the eight-metre-tall wall which loops around the West Bank city.
As the motorcade wound through the narrow streets, crowds of onlookers watched in silence.
Some held up signs of protest reading: "No return no peace."
He was briefly shown around inside the Church of the Nativity by the Palestinian president Mahmoud Abbas.