Erdogan threatens controversial new Turkish assaults on US-backed Syrian Democratic Forces

US-backed Syrian Democratic Forces (SDF) in northern Syria could soon come under attack from a joint Turkish-rebel offensive, President Recep Tayyip Erdogan warned Monday, as the campaign in Afrin winds down.

The Kurdish-dominated force has seized huge areas of northern and eastern Syria following their offensive against the Islamic State group, with US backing.

The group is dominated by the People's Protection Units militia (YPG), which lost control of Afrin this weekend following a Turkish and Syrian rebel offensive.

Erdogan warned that towns and cities held by the Kurdish fighters - such as Qamishli and Manbij and lie close to the Turkish border - could be the next target of the Ankara-led force.

"Now we will continue this process until we entirely eliminate this corridor, including in Manbij, Ayn al-Arab, Tel-Abyad, Ras al-Ayn and Qamishli," he said.

The new campaign would put Turkey on a collision course with NATO ally, the US.

Unlike Afrin - which was solely controlled by the YPG with some Russian military presence - Manbij is thought to have a US presence.

US special forces and military advisers played a key role in the SDF fight-back against IS with a Washington-led air support crucial to this victory.

Turkey had insisted its force - made up largely of Syrian rebel fighters - capture Manbij, but Washington did not believe the force couldn't succeed in taking the mixed Arab-Kurdish market town.

Qamishli, which lies on the Turkish border, is partly run by the Syrian regime.