"A suicide terrorist using a car laden with explosives attacked the western district of Qamishli," said the broadcaster, adding that at least four people were killed.

But the Syrian Observatory for Human Rights gave a higher death toll.

"At least eight members of the security forces were killed, and 15 were injured," said the Britain-based monitoring group, adding that the blast was followed by the sound of heavy gunfire.

Amateur video uploaded on YouTube by activists showed a cloud of thick smoke rising over buildings in the city.

This was the first time since the outbreak of an anti-regime revolt that Qamishli witnessed such a violent attack, Observatory director Rami Abdel Rahman said.

"It is the only city with a Kurdish majority that still has a solid security presence," Abdel Rahman added.