Al-Qaeda loyalists attacked a mainly Kurdish town in northeastern Syria sparking fighting in which 17 people were killed, two of them ambulance crew, a watchdog said on Saturday.

The assault on the strategic border town of Ras al-Ain, from which the jihadists were expelled by Kurdish militia last month, sparked an exodus of civilians into neighbouring Turkey, an activist said.

The attack on the town was part of a wider offensive by Al-Qaeda against several Kurdish majority areas of northern and northeastern Syria that began on Friday and was continuing on Saturday, the Syrian Observatory for Human Rights said.

Four Kurdish militiamen and 11 jihadists made up the rest of the dead, the watchdog said.

Syrian Kurd activist Havidar said civilians had fled "in waves into villages in Turkey."

"Intermittent clashes are continuing to take place till now, in the Asfar Najjar area and the outskirts of Tal Halaf," Havidar told AFP via the Internet.

Government troops pulled out of majority Kurdish areas of Syria last year, leaving Kurdish militia to fend for themselves.

Elsewhere in Syria, rebels attacked a pro-regime militia checkpoint in a majority Christian area of Homs province, killing six civilians and five militiamen, the Observatory said.

State news agency SANA said all those killed were civilians, and described the attackers as "terrorists".

Homs has seen some of Syria's worst violence since the outbreak of the conflict in March 2011.

Meanwhile, Amnesty International said prominent Syrian artist Youssef Abdelke and another opponent of the Damascus regime had been "subjected to enforced disappearance."

Abdelke and Adnan al-Dibs were arrested on July 18 in the Mediterranean coastal city of Tartus and have not been seen since.