US envoy in anti-IS coalition visits Turkey, one day after visiting Kurdish-controlled northern Syria

The US envoy for a coalition fighting the Islamic State group in Syria and Iraq visited Turkey on Friday, a day after visiting a Syrian Kurdish militia Ankara describes as "terrorists".

Brett McGurk's visit was not announced by the White House in advance and it comes a month after Turkish Foreign Minister Mevlut Cavusoglu called for the anti-IS envoy to be sacked.

Turkey claims he supports Kurdish militants, due to the US-led coalition's backing for the Syrian Democratic Forces, which includes the Kurdish-majority People's Protection Units.

US-backed, Kurdish-dominated forces have launched an offensive to take the Syrian city of Raqqa, which IS claims as its "capital".

Turkey has stayed away from the operation due to the involvement of Kurdish militants.

McGurk met with Cavusoglu's Deputy Undersecretary Sedat Onal, foreign ministry sources told AFP.

Turkish media said he will meet defence ministry officials.

"Pleased to be in Ankara today for consults (consulations) with NATO ally Turkey on mutual efforts to defeat ISIS (IS) and ensure it can never return," McGurk wrote on Twitter without giving further details.

Tensions between Washington and Ankara have escalated over US support for the Kurdish People's Protection Units (YPG) in Syria, which Turkey considers a front for outlawed Kurdistan Workers' Party (PKK) separatists.

The US, Turkey and the European Union have labelled the PKK a "terrorist group".

Washington has provided weapons to YPG fighters in the Syrian Democratic Forces (SDF), despite warnings from Turkey. Their offensive - with US air support - on Raqqa has so far been successful, with the fighters trapping the militants in the city after cutting the last escape route Thursday.

McGurk also visited the Kurdish and Arab controlled town of Syrian town of Tabqa on Thursday.