DAMASCUS, July 3 (Xinhua) -- A powerful explosion was heard in the northern countryside of Daraa province in southern Syria on Tuesday, which was believed to be a blast in arms depots of the Syrian army, a monitor group reported.

The explosion rocked an area where arms depots are located in the northern sector of Daraa's northern countryside near the town of Lajat, said the Syrian Observatory for Human Rights, adding that it's not yet clear whether the explosion was a result of a foreign attack or some technical error.

Other activists said Israel could be behind the bombing as it has carried out several missile attacks in the past on arms depots in Syria on the pretext that Iranian forces were located in the targeted sites.

The state media outlets are yet to comment on the explosion report.

The Observatory, meanwhile, said calm prevails Daraa province except for artillery shelling that is targeting the town of Tafas, where the militants pledged alliance with the Islamic State (IS) group.

Negotiations for settling the situation in Daraa have been ongoing between the Russian side, which is representing the Syrian government, and an array of rebel groups in that area.

The Observatory said some rebel groups accepted to reconcile with the government after handing over their weapons while the al-Qaida-linked Nusra Front and other ultra-radical groups have rejected to evacuate toward northern Syria.

The Syrian government has repeatedly accused Israel of backing the rebels in southern Syria, including in Daraa, the nearby countryside of Sweida province and in the province of Quneitra near the Israeli-occupied Golan Heights.