U.S.-backed Kurdish-led Syrian fighters are clashing with Islamic State militants north of Raqqa in Syria, a day after announcing the start of a campaign to liberate the city from the extremist group.

The Britain-based Syrian Observatory for Human Rights says fighting was underway on Monday north of Raqqa between IS and members of a coalition of Kurdish and Arab fighters known as the Syria Democratic Forces.

SDF says its fighters destroyed a vehicle rigged with explosives in a farm north of Raqqa, de IS de facto capital.

The IS-linked Aamaq news agency says IS militants hit an SDF armored vehicle north of Raqqa with a missile, killing everyone inside.

The United States, France and Britain have said they would provide air support for the Kurdish forces' offensive on Raqqa.