An explosion was heard in the northwestern province of Idlib on Saturday, in what appeared to be caused by an explosive device, a war monitor reported.

The bomb went off in the town of Sarmada in the northern countryside of Idlib near Turkey, the Syrian Observatory for Human Rights said.

The explosion caused property damage with no reports on casualties, the Observatory added.

The Britain-based watchdog group said that the explosion is part of the state of chaos and lawlessness in Idlib, which is the final major rebel bastion in Syria.

Another explosive device went off after midnight Saturday in the town of Dana in northern Aleppo, causing damage while unknown armed men opened machine guns on a military vehicle that belonged to a rival rebel group in the town.

On May 13, an explosive device went off in Sarmada a day after a roadside bomb targeted rebels' vehicle in northern Idlib.

On May 5, a suicide bomber detonated his explosive vest near a center of the Hayat Tahrir al-Sham (HTS), the umbrella group of the al-Qaida-linked Nusra Front, in the town of Dana in the northern countryside of Idlib, the Observatory said.

The Syrian army has been on an offensive against the HTS in the southern countryside of Idlib and the nearby northern countryside of Hama province in central Syria since late last month.

The HTS is the striking force in Idlib and Hama amid a state of violence resulted from the rivalry with other rebel groups in that region.