BEIRUT (Reuters) - Syrian Kurdish-led forces said on Friday that U.S. troops have started patrolling the Syrian border with Turkey to defuse tensions after threats from Ankara.

In response to questions from Reuters, a spokesman for the U.S.-led coalition said it carries out regular military visits in the region and had not increased patrols.

Turkish forces have shelled positions this week in northern Syria under the control of the Syrian Democratic Forces (SDF), which Washington trains and arms.

The SDF alliance, which the Kurdish YPG militia spearheads, returned fire and pledged to respond to any more attacks.

Ankara has repeatedly warned it would launch a cross-border offensive east of the Euphrates River in Syria if the U.S. military does not ensure the YPG’s withdrawal.

Washington’s support for the YPG has infuriated Ankara, which sees it as an extension of the outlawed Kurdish PKK movement that has waged an insurgency inside Turkey for decades.

President Tayyip Erdogan on Tuesday vowed to crush Syrian Kurdish fighters east of the Euphrates, where some 2,000 U.S. forces stand alongside the SDF.

“This morning, the (U.S.-led) international coalition held patrols monitoring the border between northern Syria and Turkey to reduce tensions,” said Mustafa Bali, head of the SDF media office.

The SDF put out a video it said showed military vehicles driving along a road in the border town of Kobani. Spokesman Kino Gabriel said new border patrols by U.S. and allied forces sought to ward off any more Turkish attacks.

“The situation is still tense, nothing is clear,” he told Reuters. “We will wait and see the result of negotiations and pressure by the Americans on the Turkish government.”

The SDF, the main U.S. partner in the fight against Islamic State, controls swathes of the north and east - the biggest chunk of Syria outside state rule.

The SDF general command said Turkish attacks led to a pause in its assault against Islamic State militants in the eastern Deir al-Zor region.

The U.S. State Department said American officials had contacted Turkey and the SDF to “emphasize the need to de-escalate the situation.”

Over the past two years, Turkish forces have swept into parts of Syria to push Kurdish fighters out of territory west of the Euphrates. Previous offensives halted at the banks of the river, partly to avoid confrontation with U.S. troops stationed further east.