Fifteen people, including 14 women, have been killed in a car bomb attack on a vehicle transporting agricultural workers in northern Syria, first responders say.

Another 15 women were wounded by the blast on the outskirts of the city of Manbij, east of Aleppo, according to the Syria Civil Defence.

The agency, which is also known as the White Helmets, said some of the wounded were in a critical condition and warned that the death toll might rise.

There was no immediate claim from any armed groups.

It was the second deadly car bomb attack in the Manbij area in three days.

On Saturday, two children and a woman were among four people killed by an explosion on a street in the city centre, the White Helmets said.