An Arab-Kurd opposition alliance seized more than a dozen villages in eastern Syria on Tuesday (February 21st) during a drive to encircle the "Islamic State of Iraq and the Levant" (ISIL) stronghold of al-Raqa, AFP reported.

The Syrian Democratic Forces (SDF) made a major incursion into Deir Ezzor province as part of their push for al-Raqa, field commander Dejwar Khabat said.

"Our aim is to cut the road to al-Raqa and besiege ISIL," he said from Makmaneh, which lies on a major highway approximately 100 kilometres east of al-Raqa city. "We have liberated 15 villages."

Khabat said ISIL was dispatching suicide bombers but had not been able to slow the offensive, which is backed by coalition airstrikes.

SDF fighters on Tuesday set up their base on a hilltop in the town of Makmaneh, digging trenches around it to prevent suicide bombers or car bombs from reaching them.

"We have entered the first villages of Deir Ezzor province," said Abu Khawlah, who heads the 1,700-strong Deir Ezzor Military Council, an Arab component of the SDF.

"Our entry into Deir Ezzor was a big surprise (for ISIL), and there will be more surprises coming," he said.

The Syrian Observatory for Human Rights said Tuesday's advance was the SDF's "biggest incursion" yet into Deir Ezzor province.