Strikes by a US-led coalition against the Islamic State (IS) group killed at least 15 civilians, including three children, in northeastern Syria on Thursday, a monitor said.
The strikes hit four IS-controlled villages in Hasakeh province, the Syrian Observatory for Human Rights said, saying the toll could rise.
It said nine IS fighters had also been killed in the strikes on the four villages.
The Britain-based monitor said the latest civilian casualties came after two days of civilian deaths in US-led strikes in Hasakeh.
It reported another eight civilians, including one woman, were killed in US-led strikes on another IS-controlled village in the province on Wednesday.
Strikes elsewhere in the province also killed 26 IS fighters on the same day, it said.
And on Tuesday, 15 civilians were killed in US-led strikes on the town of Al-Shadadi, the group said.
That brought the number of civilians reported killed in US-led strikes in Hasakeh to 38 since Tuesday.
The coalition has reportedly stepped up its raids in Hasakeh since the Kurdish-led Syrian Democratic Forces alliance launched a new operation against IS in the southern part of the province on Tuesday.