U.S. President Barack Obama and his Turkish counterpart, Recep Tayyip Erdogan, vowed to step up the fight against the Islamic State (IS) militant group and strengthen Syria's moderate opposition.
Speaking by telephone on October 15 in the wake of a major bomb attack in Ankara that killed 99 people, which Turkey has blamed on IS, they discussed the two nations' sometimes difficult joint effort to counter IS.
The call comes after Turkey complained that weapons provided by the United States to Syrian rebel groups could fall into the hands of the Kurdistan Workers Party, or PKK, and be used against Turkey.
The White House, which offered condolences for the Ankara attack on October 10, said the leaders agreed on the urgent need to stop PKK attacks in Turkey.
"The two leaders reaffirmed their shared goal of stepping up military pressure on [Islamic State] and strengthening moderate opposition elements in Syria to create conditions for a negotiated solution to the conflict, including a political transition," the White House said.
The anti-IS campaign has been complicated by Russia's support for Syrian President Bashar al-Assad and aerial bombardments of Assad foes, many of whom are supported by the United States and Turkey.