Unauthorized airstrikes by US-led coalition forces in Syria killed around 30 fighters from al-Qaeda-linked al-Nusra Front and eight civilians including children, a Britain-based group monitoring the war from the said on Tuesday.
Three children were among the eight civilians killed when strikes targeted a residential building in Aleppo province used by Nusra, the pro-opposition Syrian Observatory for Human Rights said.
The US military said in a statement it had "destroyed or damaged multiple (Islamic State) targets" around the cities of Raqqa, Deir Ezzor, Hasakah and the border town of Albu Kamal."
The targets included "(Islamic State) fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance centre, supply trucks and armed vehicles," it said.
The US military said it launched 47 Tomahawk missiles from warships in the Red Sea and North Arabian Gulf, and used remotely piloted and bomber aircraft.
Syria has long warned the United States that any strikes on its territory without Damascus's permission would constitute a violation of its sovereignty and be regarded as an act of aggression.
Damascus said the United States had informed it hours before the strikes that Islamic State targets would be hit in Raqqa, 400 kilometers (250 miles) northeast of Damascus.