US Secretary of State Mike Pompeo says an agreement with Turkey to protect Kurdish fighters in Syria after the US departure is optimistic.
He was speaking in the United Arab Emirates following a telephone call with his Turkish counterpart.
US forces in northern Syria have fought alongside a Kurdish militia against militants of the Islamic State.
Turkey, however, considers the People's Protection Units (YPG) as a terrorist group and has vowed to destroy it.
Mr. Pompeo is on tour in the Middle East to try to reassure allies after President Donald Trump's abrupt announcement last month that US forces would withdraw from Syria.
Speaking to journalists in Abu Dhabi, Pompeo said that the United States recognized "the right of the Turkish people and [Turkish President Recep Tayyip] Erdogan's right to defend his country against terrorists".
"We also know that those who fight on our side for all this time deserve to be protected as well," he said.
Pompey said he had spoken with Turkish Foreign Minister Mevlut Cavusoglu, adding: "Many details (are) still to be worked out, but I am optimistic that we can get a good result."
What did Turkey say?
Last week, President Erdogan angrily rejected requests from national security advisor John Bolton for the protection of Kurdish fighters
He claimed that such statements were "unacceptable".
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Mr. Erdogan told MPs from his ruling Justice and Development Party that the US did not know who the various Kurdish groups were, adding: "If the US considers them" Kurdish brothers ", then I am in one serious illusion. "  Mr. Bolton was visiting Ankara to look for guarantees on Kurdish fighters, but President Erdogan refused to meet him.
Turkey considers the YPG an extension of the Kurdistan Workers' Party (PKK) bandit, which has fought for Kurdish Autonomy in Turkey for three decades. The YPG denies any direct organizational link to the PKK.
The United States seeks the united front against Iran
Analysis by Barbara Plett Usher, BBC News, Riyadh
This dispute with Turkey over the American Kurdish allies has put in the vast journey to the Middle East by Pompey.
Mr. Pompey really wants to focus on the contrast to Iran. It calls for a united Arab front against what it describes as its destabilizing activity and Saudi Arabia is the key to this.
But the outrage over the Saudi murder of journalist Jamal Khashoggi has complicated the relationship. A senior US official said that the Americans want the Saudis to give a more credible explanation of what happened and do more to punish the killers, and Pompey would press them on both points
Why the United States withdraws from Syria?  In 2014, militants surpassed 100,000 sq km (39,000 square miles) from Syria and neighboring Iraq, imposing their brutal rule on nearly 8 million people. Now they control only 1% of the territory they once had.
However, the defeat of IS is far from the final. A report by the US defense department estimated in August that there would be 14,000 jihadists remaining in Syria and 17,000 in Iraq.
President Trump consequently shocked the Allies and faced severe criticism at home last month when he ordered the American forces to immediately begin to withdraw from the nearly 30% of Syria controlled by the Alliance of Syrian Democratic Forces. ; YPG (SDF).
Mr. Bolton later outlined several withdrawal conditions, which suggested that the four-month program agreed by Mr. Trump could slip.
He told reporters in Israel that this would happen in a way that "guaranteed" IS is defeated and unable to recover "and that the United States" will take care of those who fought against of us [IS] and other terrorist groups. "
What is the US presence in Syria?
It is said that about 2,000 US troops are deployed in Syria.
The ground troops first arrived in # 2015 autumn 2015 when President Barack Obama then sent a small number of special forces to train and advise YPG fighters
The United States has done this after several attempts to train and arm Syrian Arab rebel groups to fight IS militants descended into chaos.
Negl the following years the number of US troops in Syria has increased and a network of bases and airfields has been set up in an arc across the northeastern part of the country.