US Secretary of State Antony Blinken will visit Turkey on Friday to discuss the developments in Syria after the toppling of strongman Bashar al-Assad, a Turkish official source said Wednesday.

"He will be in Turkey on Friday," the source said of the visit which will come just five days after Assad`s unexpected ouster, pledging to share more details "as they are finalised".

For more than a decade, Washington has sought to keep out of Syria`s political debacle, seeing no viable partner but the lightning offensive by Islamist-led rebels is forcing a rethink, reports AFP.

There are around 900 US troops based in Syria since 2014 who have been working with Kurdish-led fighters that have battled IS jihadists in northeastern Syria.

But Washington`s support of the Kurdish forces has put it at odds with Ankara which sees them as an extension of the banned PKK which has led a decades-long bloody insurgency against the Turkish state.