The United States will strengthen its military presence in Syria to prevent Islamic State (ISIL) fighters from accessing oil fields and revenue, U.S. Secretary of Defence Mark Esper said on Friday.

"The United States will maintain a reduced presence in Syria to deny ISIL access to oil revenue," Esper told a news conference at NATO, referring to ISIL militants, saying the steps would include "some "mechanized forces" in Deir al-Zor, Syria's oil region, east of the Euphrates.

He also said Turkey had captured some escaped militants.

Damascus and Moscow deployed extra forces Friday to Syria's border with Turkey, even as Washington partially reversed a drawback to boost its own military presence near key Syrian oil fields.

U.S. authorities must extradite the commander of the Kurdish-led SDF to Turkey when he enters the United States, Turkish Justice Minister Abdulhamit Gul said Friday after Ankara slammed Washington for treating him as a "legitimate political figure."

U.S. President Donald Trump on Thursday said he had talked with Mazlum Abdi, commander of the Syrian Democratic Forces (SDF) which fought against extremists in Syria and that he had "really enjoyed" the conversation.

In a tweet on Wednesday, Trump thanked Mazlum and said: "I look forward to seeing you soon," raising fears in Turkey of a possible face-to-face meeting between the two men in the United States.

"If you start legitimizing terrorists like this, tomorrow you will end up meeting with Baghdadi as well," Turkish Foreign Minister Mevlut Cavusoglu said in televised remarks.

U.S. senators urged the State Department on Wednesday to quickly provide a visa to General Mazloum Kobani so he can visit the United States to discuss Syria.

Speaking to reporters, Gul said Turkey will demand that U.S. authorities detain Mazloum as soon as he enters the United States. He said the foreign ministry had conveyed the extradition request to the United States.

"We have informed the US of all of this in a written note," the minister added.

Relations between Turkey and the US are particularly tense after Ankara launched a cross-border offensive on October 9 against the Kurdish YPG militia, whose fighters make up the bulk of the SDF.

The United States earlier this month announced a pullout from Kurdish-held areas in northeast Syria, allowing Damascus, Ankara and Moscow to carve up the Kurds' now-defunct autonomous region.

(With input from Reuters, AFP)

(Cover: A U.S. military vehicle patrols a road near the town of Tal Baydar in the countryside of Syria's northeastern Hasakeh province, October 12, 2019. /VCG Photo)