The Syrian Democratic Forces (SDF) has stopped all joint counter-terrorism operations as a result of Turkish bombardment on its area of control, spokesman Aram Henna said Friday.

SDF is a US-backed group that helped defeat ISIS militants in Syria.

Henna told Reuters that "all coordination and joint counter-terrorism operations with the coalition" as well as "all the joint special operations we were carrying out regularly" had had been halted.

Turkey has ramped up its shelling and air strikes on northern Syria in recent weeks and is preparing a ground invasion against Syrian Kurdish fighters that it dubs terrorists but which make up the bulk of the US-supported SDF.

The SDF has long warned that fighting off a new Turkish incursion would divert resources away from protecting a prison holding ISIS militants or targeting ISIS sleeper cells still waging hit-and-run attacks in Syria.

Pentagon spokesman Brigadier General Patrick Ryder earlier told reporters that operations against ISIS had not stopped.

SDF head Mazloum Abdi earlier this week told Reuters he wanted a "stronger" message from Washington after seeing unprecedented Turkish deployments along the border.

"We are still nervous. We need stronger, more solid statements to stop Turkey," he said. "Turkey has announced its intent and is now feeling things out. The beginning of an invasion will depend on how it analyses the positions of other countries."