Rebels killed a relative of Syria's political security chief Rustom Ghazali, a key regime figure, wounded another and kidnapped a third on Friday in the southern province of Daraa, a watchdog said.

State television also reported the attack, without mentioning the family ties between Ghazali, a Sunni Muslim, and the three men.

"An armed terrorist group attacked a number of people at a petrol station near the village of Qarfa, which led to the killing of one and the wounding of another," Syria TV said, identifying the dead man as Hussam Ghazali.

It said the victim's father Fayez was wounded, and Jalal Ghazali was abducted.

The Syrian Observatory for Human Rights gave the same report, but quoted local activists as saying the three men were relatives of Major General Rustom Ghazali.

It said rebels had attacked the Ghazali compound on the outskirts of Qarfa alongside the Daraa-Damascus highway.

According to the Syrian Revolution General Commission, Free Syrian Army rebels targeted a "gathering of security forces and shabiha (militiamen) in the Ghazali complex before noon."

Rustom Ghazali's nephew was killed, while his brother was wounded and another nephew was kidnapped, it said.

"The siblings of Major General Ghazali and their children were the worst shabiha for the people of the town of Qarfa and the province as a whole," the activist network quoted residents as saying.

Daraa native Ghazali, 59, has been political security chief since his predecessor and three other senior security heads were killed in a Damascus bombing in July 2012.

Ghazali was the head of military intelligence in Lebanon from 2002 to 2005, when Syrian troops withdrew from its tiny neighbour after occupying it for three decades.