US-backed Kurdish fighters in northern Syria are heading to the Turkish-assaulted Kurdish enclave of Afrin, leading to an "operational pause" in their operations against the Islamic State group, the Pentagon said Monday.

The Syrian Democratic Alliance, made up mainly of Kurds as well as Syrian Arabs, is the main ground force that the US has been training and supporting to battle IS.

While most of the land once held by the jihadists has been recaptured, the extremists remain entrenched in the Middle Euphrates River Valley (MERV).

Some SDF in the area have now gone to Afrin, where Turkish troops and allied rebels have for six weeks been attacking Kurdish People's Protection Units (YPG) militia in the enclave.

"Operational pauses occur regularly for a variety of reasons," Pentagon spokesman Colonel Rob Manning said.

"The nature of our mission in Syria has not changed. … This operational pause will not cause us to lose sight on our main objective, which is ISIS."

Major Adrian Rankine-Galloway, also a Pentagon spokesman, said the US was continuing its own operations against IS, and none of the territory recaptured from IS had been lost.

"We are aware of the departure of some SDF forces from the Middle Euphrates River Valley and continue to point out the potential costs of any distraction from the defeat-ISIS fight," he said, adding that the SDF was "continuing to contain and degrade ISIS in the Middle Euphrates River Valley."

The acknowledgement that some SDF fighters are peeling away from the fight in the MERV comes after the head of Central Command, General Joe Votel, warned lawmakers of "diverging interests" in the region.

"Our concern, of course, is that this activity in Afrin is detracting from our efforts against ISIS," Votel told the House Armed Services Committee last week.

Turkey strikes kill 19 civilians in Syria's Afrin: monitor
Beirut (AFP) March 5, 2018 –

Turkish air strikes on Monday killed 19 civilians including two children in northwestern Syria's Kurdish enclave of Afrin, a monitor said.

The deadly air raids hit the town of Jandairis near the Turkish border, the Britain-based Syrian Observatory for Human Rights war monitor said.

They come six weeks into a Turkey-led assault against the Kurdish People's Protection Units (YPG) militia in the enclave.

Jandairis has come under heavy fire since dawn on Monday as Turkish troops and allied rebels on its edges seek to retake the area from Kurdish fighters, Observatory head Rami Abdel Rahman said.

Since the Turkish offensive started on January 20, Turkish bombardment has killed more than 170 civilians, including 29 children, the Observatory says.

Turkey denies the reports and says it takes the "utmost care" to avoid civilian casualties.

The monitor says 270 pro-Ankara rebels and nearly 310 Kurdish fighters have also lost their lives.

At least 40 Turkish soldiers have also been killed since the start of the assault, according to Ankara.

Since pro-regime fighters were deployed to help the Kurds in Afrin last month, some 58 of these "popular forces" have been killed, it said.

Ankara says the YPG is a "terrorist" extension of the Kurdistan Workers' Party (PKK), which has waged a three-decade insurgency against the Turkish state.

But the YPG has been a key component of a US-backed Kurdish-Arab alliance that has been fighting the Islamic State jihadist group in Syria.

More than 340,000 people have been killed since Syria's war started in 2011. It has since spiralled into a complex conflict involving world powers.