Men inspect a dead body at a site damaged by what activists said was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad in Aleppo's Kallaseh neighbourhood June 21, 2014. REUTERS/Hosam Katan

Syrian jets bombed the border area with Iraq Saturday, stepping up attacks against the Islamic State in Iraq and Syria, which has captured a large swath stretching from Syria through northern Iraq.

Reuters reported at least 16 people were killed and dozens injured in the five bombing raids over residential areas of Muhassan, just 60 miles from the Iraqi border. The bombing occurred just a day after the town's elders pledged their support to ISIS.

"(Syrian President Bashar) Assad's forces want to punish towns such as Muhassan for their support of ISIS. This bombing campaign is lending a hand to help Iraqi Shiite leader (Prime Minister Nouri al-) Maliki to destroy ISIS after its victories," said Abdullah al-Mashour, an ISIS sympathizer from the town of Muhassan, by Skype.

The Sunni insurgents already control 70 percent of Deir Zor province, rebel sources told Reuters, and are pushing to control the remaining area, which is a rich source of oil and grain silos.

"Their aim is to link these areas with Iraq's Anbar," said Abu Thaher, a resident of Deir Zor contacted by Reuters on Skype.

ISIS seized al-Qaim, which is just across the border from Deir Zor, Friday and moved into a border crossing once guards heard the town had fallen and fled. The seizure of al-Qaim gave ISIS control over four cities in Anbar province in Iraq and a highway leading from Syria to Baghdad, CNN reported.