Turkey's President Tayyip Erdogan said the United States has failed to comply with the timescale agreed for the withdrawal of Kurdish YPG militia from the northern Syrian city of Manbij, the Hurriyet newspaper reported on Friday.

As agreed by the two NATO allies in June, Turkish and U.S. forces are now carrying out patrols in Manbij to clear the area of YPG, a group that Turkey views as a terrorist organisation linked to Kurdish militants on its own soil.

But Erdogan said YPG forces remain in Manbij, and accused the United States of not holding to commitments under the roadmap agreed in June.

"The United States certainly did not comply with the agreed calendar of the Manbij roadmap; YPG did not exit the area. The real owners of the region are not settled in yet," Erdogan was quoted as telling reporters following his recent visit to New York to attend the United Nations General Assembly.

"The United States did not keep their promise here."

Turkey has been infuriated with Washington's support for the YPG militia and prior to the June agreement it had threatened to push on with a ground offensive against YPG in Manbij despite the U.S. troops stationed.

Before the agreement with Washington, Turkey had carried out two cross-border operations against the YPG in Syria.

Erdogan also said that Turkey was prioritising the disposal of heavy weaponry held by "radical" rebel forces in Idlib in northwest Syria, where Russian and Turkish troops trying to enforce a new demilitarised zone.

"We attach great importance to the disposal of heavy weaponry of radical groups. The majority of the burden is on our intelligence agency. The efforts are going well," Erdogan said.

Under the plan, the rebels will be required to withdraw from Idlib by the middle of next month.