The Syrian Democratic Forces (SDF) on Thursday (December 13th) moved deep into Hajin, the main village in the last pocket still held by the "Islamic State of Iraq and Syria" (ISIS) in eastern Syria, AFP reported.

The Arab-Kurdish alliance, with support from airstrikes conducted by the international coalition, deployed across the Euphrates Valley village.

"The SDF managed to break the defences of ISIS after massing a large number of fighters backed by the international coalition," the Syrian Observatory for Human Rights said.

"They achieved quick progress inside Hajin, the largest of the villages that were controlled by ISIS," Observatory head Rami Abdel Rahman said.

The SDF said on social media they had "liberated the city centre of Hajin and the big mosque".

Hajin lies on the east bank of the Euphrates in the eastern province of Deir Ezzor, about 30 kilometres from the border with Iraq.

The SDF launched an operation in September to flush out ISIS but their advance has been fraught with obstacles.

"Now ISIS is confined to tunnels and to the edges of town," Abdel Rahman said.

"Fighting on the ground and airstrikes are continuing. The mines planted by the jihadists are the main remaining obstacle," he said.