"Twenty-six IS family members including 14 children and 9 women were killed in coalition air strikes on Friday morning on the town of Hajin," the Syrian Observatory for Human Rights said.

On Thursday, coalition raids killed another seven civilians in the nearby village of Al-Shaafa, Observatory chief Rami Abdel Rahman said.

Both Hajin and Al-Shaafa are in a last pocket under IS control in the eastern province of Deir Ezzor near the border with Iraq.

A coalition spokesman did not immediately reply for a request for comment.

The coalition has been backing a Kurdish-Arab alliance fighting the jihadists in the area.

IS overran large swathes of Syria and neighbouring Iraq in 2014, proclaiming a "caliphate" in land it controlled.

But the jihadist group has since lost most of it to various offensives in both countries.

In Syria, the group has seen its presence reduced to parts of the vast Badia desert and the pocket in Deir Ezzor.

Since 2014 the US-led coalition has acknowledged direct responsibility for more than 1,100 civilian deaths in Syria and Iraq, but rights groups put the number killed much higher.

The Syrian Observatory for Human Rights says coalition strikes in Syria alone have killed more than 3,300 civilians.

Syria's war has killed more than 360,000 people since it erupted in 2011 with the brutal repression of anti-government protests.