The Syrian Democratic Forces (SDF) seized the main hub of Hajin from the "Islamic State of Iraq and Syria" (ISIS) on Friday (December 14th), a milestone in the operation to eradicate the group from eastern Syria, AFP reported.

The Arab-Kurd alliance secured Hajin, the largest settlement in what is the last pocket of territory controlled by ISIS, the Syrian Observatory for Human Rights said.

"After a week of heavy fighting and airstrikes, the SDF were able to kick ISIS out of Hajin," said Observatory head Rami Abdel Rahman.

The operation was completed at dawn, he said, a day after SDF forces fanned out across the large village in the Euphrates valley.

On Thursday, the last ISIS fighters were confined to a network of tunnels and the edges of Hajin, which lies in the eastern province of Deir Ezzor, about 30 kilometres from the border with Iraq.

The area held by ISIS is sometimes referred to as the "Hajin pocket", the last rump of the area the group once controlled in swathes of Syria and Iraq.

ISIS fighters pulled back to positions east of Hajin Friday and to al-Sousa and al-Shaafa, the two other main villages in their shrinking Euphrates valley enclave.

According to Abdel Rahman, a total of 17,000 fighters from the SDF are involved in the operation, launched September 10th, to flush ISIS out of its last bastion.

At least 900 ISIS elements and 500 SDF fighters were killed in the fighting, the Observatory said.

Besides what is left of the pocket near Hajin, ISIS has a presence in Syria's vast Badiya (desert), as well as sleeper cells across Iraq and Syria that regularly carry out attacks.