One Turkish soldier was killed and another was wounded on Sunday after an attack by the Syrian Kurdish YPG militia in northeast Syria's Tel Abyad, the Turkish defence ministry said, despite a deal to pause military operations as militants withdraw from the area.

Turkish President Tayyip Erdogan agreed on Thursday in talks with US Vice President Mike Pence a five-day pause in the offensive to allow time for the Kurdish fighters to withdraw from a “safe zone” Turkey aims to form in northeast Syria near its border.

On Saturday, the truce was holding along the border, with just a few Turkish military vehicles crossing, a Reuters reporter at the scene said. But Sunday's attack has underlined how fragile the agreement is.

Ankara regards the YPG, the main component of the Kurdish-led Syrian Democratic Forces (SDF), as a terrorist group because of its links to Kurdish insurgents in southeast Turkey. The YPG has been a close US ally in the fight against the militant Islamic State (IS) group.

In a statement, the Turkish defence ministry said an attack by the YPG with anti-tank and light weapons had struck Turkish soldiers carrying out a reconnaissance and surveillance mission in Tel Abyad on Sunday.

“The immediate response based on self-defence was given,” the ministry said. “Despite the Safe Zone Agreement with the United States... 20 harassments/violations were committed by PKK/YPG terrorists,” it said.

On Friday, the Kurdish militia had accused Turkey of violating the five-day pause by shelling civilian areas in the northeast and the border town of Ras al Ain.

A senior Turkish official later dismissed the accusations on Saturday, saying these were an attempt to sabotage the agreement between Ankara and Washington, and that Turkey fully supported the deal.

“Crush the heads”

Erdogan had warned on Saturday that the offensive would continue and Turkey would “crush the heads of terrorists” if the deal was not fully implemented, while Turkey insisted that it is the duty of Washington to ensure the withdrawal of the YPG.

Turkey's defence ministry said late on Saturday that it was closely monitoring the withdrawal of the YPG and that it was in close contact with US officials over the issue and to provide logistical information.

Turkey aims to establish a “safe zone” some 32 km (20 miles) into Syria. Erdogan said on Friday it would run for some 440 km along the border, though the US special envoy for Syria said the accord covered a smaller area where Turkish forces and their Syrian rebel allies were fighting.

Erdogan also said on Friday that Turkey would set up a dozen observation posts across northeast Syria, and that he would hold talks with Russian President Vladimir Putin on what steps to take in the planned “safe zone” next week.