Armed tribes supported by Syria's Islamist-led government clashed with Druze fighters in the community's Sweida heartland on Friday, a day after the army withdrew under Israeli bombardment and diplomatic pressure.

The United Nations called for an end to the "bloodshed" and demanded an "independent" investigation of the violence, which has claimed at least 638 lives since Sunday, according to the Syrian Observatory for Human Rights.

The renewed fighting raised questions over the authority of interim leader Ahmed al-Sharaa, whose interim government also has difficult relations with the Kurdish and Alawite minorities.

It was Sharaa who ordered government forces to pull out, saying that mediation by the United States and others had helped avert a "large-scale escalation" with Israel.

An AFP correspondent said renewed fighting erupted on Friday between Bedouin tribal factions and the Druze at the entrance to Sweida, where about 200 tribal fighters clashed with armed Druze men from the city using machine guns and shells.

The Syrian Observatory for Human Rights also reported fighting and "shelling on neighbourhoods in Sweida city."

The UN's International Organisation for Migration on Friday said, "79,339 people have been displaced since 13 July, including 20,019 on 17 July."

Israel, which bombed the Syrian military in Sweida and Damascus earlier this week to put pressure on the government to withdraw, said on Friday that it was sending aid to the Druze community in Sweida.

A ceasefire was supposed to take effect on Thursday, but Sharaa's office accused Druze fighters of violating it. (AFP)