BEIRUT: At least 56 people have been killed in a week of fighting in northeast Syria between anti-government rebels and members of the long-oppressed Kurdish minority who have seized on the civil war to try to secure self-rule, activists said on Tuesday.

The British-based Syrian Observatory for Human Rights, which collates reports on Syria's violence from local activists, said on Tuesday that the anti-Damascus rebels were using tanks and mortars on Tuesday against Kurdish forces.

In a separate incident, it said at least 42 people including women and children had been killed when a car bomb targeting a pro-government militia went off on Monday evening in the town of Salamiyah, east of the central city of Hama.

With Arab rebels entangling government forces to the west and south, the Kurds, who make up around 10 percent of the population, have exploited the vacuum to set up the Kurdish schools and cultural centres long denied them under Baath party rule, as well as police and armed militias.

But they have remained at arm's length from the increasingly Islamist-dominated mostly Sunni Arab rebels, fearing that these would not honour the autonomy aspirations of a region that holds a significant part of Syria's estimated 2.5 billion barrels of crude oil reserves.

On Tuesday, fighters of the Kurdish People's Defence Units clashed with several rebel groups in the city of Ras al-Ain in Syria's northern Hasaka province, the Observatory said.

"The clashes erupted (last) Wednesday ... and (have) resulted in the deaths of at least 56 fighters," the group said.

The fighting is one of many sectarian or ethnic fault lines that have prevented the emergence of a single coherent movement to try to oust President Bashar al-Assad since insurgents took up arms after the government cracked down on peaceful protests in March 2011.

Since then, the conflict has become a full-scale civil war in which more than 60,000 people have been killed, 650,000 pushed to flee the country and well over a million made homeless within Syria.

A video posted online showed men and women gathering around a street strewn with rubble at what the Observatory said was the site of the blast in Salamiyah.

It said some of the wounded were in critical condition.

The state news agency SANA said the blast had been caused by a suicide bomber and that 25 people had been killed.

Reuters cannot verify such reports from inside Syria because the government severely limits access for independent media.