Washington and Ankara are bitterly at odds over US support for the Kurdish People's Protection Units (YPG) in Syria.
Washington and Ankara are bitterly at odds over US support for the Kurdish People's Protection Units (YPG) in Syria, which Turkey considers a front for banned Kurdistan Workers' Party (PKK) separatists.
"Brett McGurk is definitely giving support to PKK and YPG. It would be useful if this person was replaced," Foreign Minister Mevlut Cavusoglu told NTV television.
Last year, McGurk visited YPG members who controlled the Syrian town of Kobane and was awarded a plaque, which drew Turkey's wrath.
President Recep Tayyip Erdogan angrily told Washington at the time to choose between Ankara and "terrorists".
But Ankara is now upbeat about the future of relations with Washington under President Donald Trump, with Cavusoglu praising the new administration as "more sincere" after Erdogan's talks with the US leader this week.
Erdogan met Trump at the White House on Tuesday, with the two leaders pledging to improve ties between the NATO allies -- even as Erdogan gave a stern warning about Washington's arming of Kurdish militia in Syria.
"It is absolutely unacceptable to take the YPG-PYD into consideration as partners in the region, and it's going against a global agreement we reached," Erdogan said in Washington, referring to the Kurdish Democratic Union Party, whose armed wing is the YPG.
The United States sees the YPG as the most effective force on the ground in the fight against Islamic State militants.
Turkey is keen to join a future battle to recapture the de facto IS capital of Raqa in Syria, but only if Kurdish militia forces do not participate.
US officials told Ankara that the YPG would not constitute a threat for Turkey and that arms supplied by Washington would be used in Raqa and in the south, not against Turkey, Cavusoglu said.
Speaking to reporters at the Turkish embassy in Washington, Erdogan said he told Trump that if there were a YPG attack, Ankara would act unilaterally.
"We clearly told them if there is any attack by the YPG against Turkey, we will apply the rules of engagement without asking anyone," he was quoted as saying by the Hurriyet newspaper Thursday.
Erdogan also said that the US had made up its mind on Raqa, which meant Turkey could not join the operation "under the current circumstances," referring to the YPG's involvement.
But Erdogan said he believed Washington "will knock our door on the issue of Syria."
McGurk was in northern Syria Tuesday and Wednesday for talks with the leadership of the Syrian Democratic Forces, an alliance of Arab and Kurdish fighters, and the YPG, according to a source in the nascent Raqa city civilian council.
The council has been set up to manage the city once IS fighters have been ousted.
The meetings which took place in Kobane and Ain Issa focused on "the plan of attack on Raqa and providing support for people fleeing the fighting," the source said.