A ferocious battle on the outskirts of the northern city of Raqa, near the Turkish border, killed dozens of Syrian troops and rebel fighters on Saturday, a watchdog reported.

"Fierce clashes pitting rebel fighters from several battalions against regular troops have raged since dawn on the outskirts of Raqa city... explosions could be heard in the city, and towers of smoke could be seen rising into the sky," said the Syrian Observatory for Human Rights.