Smoke rose from burning houses in south Syria's Sweida on Saturday and an Arab tribal fighter vowed to "slaughter" residents as deadly clashes with Druze fighters persisted.

Just hours earlier, Syrian interim President Ahmed al-Sharaa had announced an immediate ceasefire, but Bedouins and tribal fighters who are allied with the Syrian authorities pushed on in the west of the Druze-majority city.

"Go forward, tribes!" said fighter Abu Jassem, addressing fellow combatants in the area, where the streets were largely deserted.

"We will slaughter them in their homes," he said, referring to the Druze.

The tribal fighters have converged on Sweida from other parts of Syria to support the Bedouins who have been clashing with Druze fighters since July 13.

The violence has killed at least 940 people, according to a monitor.

An AFP correspondent on Saturday saw dozens of torched homes and vehicles and armed men setting fire to shops after looting them.

Some fighters, their faces covered, opened fire in the streets with automatic weapons while others moved around on vehicles and motorbikes.

One fighter wore a black band around his head that bore the Islamic profession of faith.

Another was carrying scissors, after footage in recent days showed fighters cutting the moustaches of Druze elderly and clergy, a grave insult to members of the minority community.

The Druze, followers of an esoteric religion that split from Shiite Islam, are regarded at best with suspicion by more hard-line Sunni Islamists who count among the ranks of Syria's new authorities.