A suspected US-led coalition strike in Syria's Raqqa province has killed 12 women, the Syrian Observatory for Human Rights said this morning.

The Britain-based monitor said the strike yesterday afternoon hit vehicles carrying farm workers home from fields in the east of the province.

The monitor said it believed the strike had been carried out by the US-led coalition fighting the so-called Islamic State militant group in Syria and Iraq.

The group also said that a second coalition strike on a town near the Iraqi border killed a further 23 civilians.

The strike hit the town of Albu Kamal in the early hours of the morning, Observatory director Rami Abdel Rahman said.

The Observatory relies on a network of sources inside Syria and says it determines whose planes carry out raids according to their types, locations, flight patterns and the munitions used.

IS has lost swathes of the territory it once held in Raqqa province, though it still holds Raqqa city and some areas to the east.

A US-backed alliance of Kurdish and Arab fighters known as the Syrian Democratic Forces is battling towards Raqqa city, the jihadist group's most important remaining Syrian bastion.

The US military said in May that coalition strikes in Syria and Iraq had "unintentionally" killed 352 civilians since it launched operations against IS in 2014.

Rights groups say the actual figure is much higher.