The visit appeared to be the first by a senior US government official inside Syrian territory.

McGurk, who is US President Barack Obama's envoy to an international coalition fighting IS in Syria and Iraq, was accompanied by French and British officials, the sources told AFP.

One Kurdish source close to the meeting said a "high-level military delegation from the international coalition (against IS)," met Saturday with senior members of the Syrian Democratic Forces (SDF) alliance.

The source said the talks in the Kurdish town of Kobane covered "military plans" for the fight against IS.

"These meetings will have an impact on many developments that will be seen in the area," he added, without providing further details.

The talks were confirmed by a second Kurdish source on the ground and reported in Kurdish media.

Contacted by AFP, the US State Department was not immediately able to confirm or deny the reported visit.

The SDF is an alliance of Syrian Kurds and Arabs who are fighting IS with support from the US-led coalition.

It is composed mostly of the Kurdish People's Protection Units (YPG), a powerful militia that has proved Syria's most effective force against IS, along with smaller units of Syrian Arab Muslim and Christian fighters.

The meetings come after the YPG's political wing, the Democratic Union Party (PYD), was excluded from new peace talks in Geneva being organised by the UN.

Despite cooperation between the US-led coalition and the YPG in the fight against IS, the Kurdish militia and its political branch face fierce opposition from neighbouring Turkey.

Ankara considers the PYD and YPG to be affiliates of the outlawed Kurdistan Workers Party (PKK), which has waged an armed insurgency in Turkey, while Syria's opposition accuses them of being too close to the regime in Damascus.

But the coalition has worked closely with the YPG since it launched air strikes in Syria in September 2014, expanding a campaign that began in Iraq a month earlier.

And that support has continued since the formation of the SDF last October, with US-led air support helping the alliance seize a key dam from IS last month.

US-based Kurdish affairs analyst Mutlu Civiroglu said McGurk's visit appeared intend to assuage the Kurds after their exclusion from the Geneva talks.

"The goal is to ease Kurdish anger and give them reassurances that they are not being ignored and that they have a part in this process," he said.

Kurdish sources earlier told AFP that US Deputy Secretary of State Tony Blinken had called PYD chair Saleh Muslim to discuss Washington's view on the Kurdish issue and the peace talks.