Turkey threatens to target Kurdish forces in Syria's Manbij

Turkish forces might next target the Kurdish-held town of Manbij in northern Syria alongside Ankara's current campaign in Afrin, Turkey Foreign Minister Mevlut Cavusoglu said Tuesday.

"This operation is targeting [the] Afrin region but the threats are also coming from Manbij," Cavusoglu told France 24.

"We, as Turkey, have to eliminate (threats) where ever there are threats. For now Afrin is the target but in the future we might also start an operation in Manbij and also in the eastern part of the Euphrates."

Ankara began "Operation Olive Branch" on Saturday with troops and Syrian rebels moving into north-west Syria's Afrin, an enclave of the Kurdish People's Protection Units (YPG).

Backed by air strikes and artillery, the force had made gains in the area but civilian casualties have mounted bringing mild criticism from Turkey's NATO allies.

Washington has been a key backer of the Syrian Democratic Forces - which the YPG plays a major role in - who have battled the Islamic State group in northern Syria.

If Turkey were to fight the force in Manbij - a town to the east in territories controlled by the SDF - it would likely bring further anger from the US.

US President Donald Trump is expected to voice alarm to his Turkish counterpart Recep Tayyip Erdogan on Wednesday about the war.

In his strongest comments yet on the offensive, US Defence Secretary Jim Mattis called for Turkey to show "restraint".

Manbij is still a campaign Ankara has not ruled out.

"This current operation is targeting Afrin region. But in the future, if the threat continues to come from other regions, we might also eliminate terrorist groups in other parts as well," Cavusoglu added. Four days of fighting has cost the lives of 43 pro-Ankara Syrian rebels, 38 Kurdish fighters, one Turkish soldier and 28 civilians.