Those killed in the village of Al-Shaafa on Sunday included 32 civilian members of IS families, the Syrian Observatory for Human Rights said.

Thirteen children were among the victims, the Britain-based war monitor said.

"The strikes targeted IS homes in Al-Shaafa," Observatory chief Rami Abdel Rahman said, inside a last pocket under jihadist control in the eastern province of Deir Ezzor.

The bodies could not be retrieved earlier because air raids were ongoing, he said.

A coalition spokesman did not immediately reply for a request for comment, but has previously said that it would investigate any credible claims of civilian casualties.

The coalition has been backing a Kurdish-led alliance called the Syrian Democratic Forces fighting the jihadists.

The SDF late last month suspended its fight against IS in protest at Turkish shelling of Kurdish militia positions along Syria's northern border.

But they said on Sunday they were resuming their battle after "intensive contacts" with the international coalition and "strong diplomatic activity" to defuse the crisis.

IS overran large parts 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.

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