Syrian President Bashar al-Assad. Photo: Wikimedia Commons.

Syrian jets struck rebel-held towns in the country’s south on Monday, the first aerial attacks on the area since the United States and Russia brokered a deal making it a “de-escalation zone” last year, rebels and residents said.

At least eight raids struck the rebel-held towns of Busr al-Harir, Hrak, al-Gharaiya al-Gharbiya and al-Sowara in rural areas in eastern Deraa province in southern Syria, two rebel officials told Reuters.

The southern area around Deraa province is one of three main parts of the country where large populations are still under the control of rebels opposed to President Bashar al-Assad, along with a northern area near the Turkish border and the eastern Ghouta region on the outskirts of Damascus.

Government forces have focused their efforts on eastern Ghouta since mid-February, launching one of the fiercest campaigns of the war now entering its eighth year.

One rebel commander said the strikes in the south appeared to be a warning to rebels under the Free Syrian Army (FSA) umbrella who were planning to wage an offensive in coming days to relieve pressure on their comrades in eastern Ghouta.

“We were starting an operation, and we had not announced zero hour, and the regime preempted us,” said Abu Nabout, a military commander in Liwa Tawheed al-Jnoob, a rebel faction in the FSA rebel alliance.

Russia, which backs Syria’s government in the civil war, and the United States, which has backed rebel forces seeking to topple Assad, met secretly in Jordan in June and announced a ceasefire in Syria’s southwest a month later.

The truce had reduced fighting there and was meant to lead to a longer-lasting de-escalation, a step towards a full settlement.

Rebels have long feared Syria’s army will return to attack them once it has consolidated gains in the north and other areas. Insurgents say the de-escalation zones free up Syria’s army to make territorial gains elsewhere.

Hundreds of thousands of people have been killed and more than 11 million made homeless in Syria’s multi-sided civil war. The government has made huge territorial gains since Russia joined the fighting on the side of Assad in 2015.