AMMAN (Reuters) - At least five people were killed and scores wounded on Wednesday in a bomb attack on a local administrative office in the Kurdish-held Syrian town of Tel Abyad, near the Turkish border, witnesses said.

They said a suicide car bomber attacked the building run by Kurdish local authorities in the town, which was captured by the Kurdish YPG militia last year from Islamic State militants in an offensive backed by U.S.-led air strikes.

Tel Abyad lies north of Raqqa and had been a key supply line for the Islamic State stronghold.

The Britain-based Syrian Observatory for Human Rights later said at least 10 people were killed in the blast with nine wounded, some seriously.

Amaq news agency, affiliated to Islamic State, said militants detonated a car near a gathering of YPG fighters near the old local parliament building in the city center.

The YPG is one of the most powerful militias in Syria and seen as the backbone of the Syria Democratic Forces, whose campaign to seize Islamic State controlled Manbij is supported by U.S.-led air strikes and American special forces.

Islamic State militants have carried out more car bombings in Kurdish controlled areas after losing significant territory in northeastern Syria.

(Reporting by Rodi Said in Kobani, Syria; Writing by Suleiman Al-Khalidi; Editing by Janet Lawrence)