Heavy Turkish shelling across the border into Syria killed six US-backed Kurdish fighters and wounded several civilians, a monitoring group said on Thursday.

The artillery fire struck the Kurdish-controlled Afrin area in the northwest late on Wednesday, the Syrian Observatory for Human Rights said.

A Syrian Kurdish news website reported the same death toll.

The majority-Kurdish Afrin area has been under the control of the Kurdish People's Protection Units (YPG) since government forces pulled out in 2012.

It has come under intermittent artillery fire by Ankara which regards the YPG as an extension of the outlawed rebel Kurdistan Workers Party (PKK) that has been waging an insurgency in southeastern Turkey for three decades.

But it has not been a direct target of the unprecedented ground incursion which Ankara launched on August 24 targeting both the YPG and the Islamic State jihadist group.

Turkish leaders have said a major goal of the intervention was to prevent the YPG and their allies from joining up the Afrin enclave with the large swathe of territory they control in northeastern Syria to create a contiguous autonomous region along much of the border. 

A total of 19 Kurdish and allied fighters have been killed since the incursion began, according to the Observatory.

Turkish troops and their Syrian rebel allies have now occupied a border strip stretching from the Euphrates River to the Afrin enclave, after ousting the last IS fighters last weekend.

Turkish operations against the YPG have drawn criticism from Washington which has urged both sides to focus their sights on IS.

Washington regards the Kurdish militia as the most effective force fighting IS on the ground in Syria and has provided it with weapons and military advisers.

Source: AFP