At least 14 people have been killed in the attacks which targeted rural areas in the northern and eastern part of the Daraa province in southwestern Syria.
British-based war monitor Syrian Observatory for Human Rights said on Thursday Syrian regime forces have resumed their strikes on several opposition-held areas in Daraa province in Southern Syria.
The monitor said recent strikes on Daraa have killed at least 14 people, 8 of them are civilians and the rest US and Jordanian-backed opposition fighters.
SOHR said that the ongoing escalation in the south has forced more than 12,500 people to flee Daraa province fearing an upcoming ground offensive by regime forces on the area.
Syrian regime forces and their Iranian-allied militias have deployed a large number of troops to the south preparing for a major ground offensive against opposition groups in the area.
Opposition-held areas in south are considered a part of the "de-escalation zone" deal that was agreed upon by Turkey and Russia as guarantors during Astana talks last year.
Local sources in the area told Anadolu Agency on condition of anonymity that Hara, Nahta, Bushra Harir, Dellafai Miskiya and Hirak areas have been under intense bombardment from regime forces.
The offensive in the southwest would risk a major escalation of the seven-year-old war.
The area has a strategic importance for Israel, which is deeply alarmed by Iranian influence in Syria.
Washington has warned it would take "firm and appropriate measures" in response to violations of the "de-escalation" deal.
US-allied Jordan is increasingly worried about a spillover of violence and has been engaged in stepped up diplomatic efforts to preserve the de-escalation zone which it also helped to broker last year, a Jordanian source said.
Rebels say Iranian-backed forces allied to regime leader Bashar al Assad have boosted their numbers in the area, though a commander in the regional alliance fighting in support of Assad denied Tehran-aligned forces had a big presence there.