A suicide car bombing in Qamishli, a Kurdish city in northern Syria, killed at least four people on Sunday, state television reported, but a human rights group said that eight members of the security forces died in the blast.
"A suicide terrorist using a car laden with explosives attacked the western district of Qamishli," said the state broadcaster, adding that at least four people were killed.
But the Syrian Observatory for Human Rights gave a higher death toll and said the attack targeted a security headquarters.
"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 heavy gunfire.
Amateur video uploaded on YouTube by activists showed a cloud of thick smoke rising over 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 said, adding that the target of the blast was a regional security headquarters for Kurdish districts.
Abdel Rahman said that the military pulled out of Kurdish regions in the north, including Qamishli, several months ago and that the rebel Free Syrian Army has no presence whatsoever in the city. But a small number of autonomous fighters are still there.
Residents of Qamishli said they were terrified by the force of the blast.
"The earth shook beneath us, the force of the explosion was immense," said an activist who identified himself as Serdar.
"I was at a nearby hospital at the time of the blast," Serdar told AFP via the Internet. "Many injured people were rushed to the hospital for treatment. There was broken glass on the streets. God protect Qamishli."
"I spoke to my family, who lives around three kilometres (two miles) from the site of the blast. They were terrified," exiled Kurdish activist Massoud Akko told AFP via the Internet.