Jihadists have executed 17 men in recent days in areas they control in eastern and northern Syria to avenge a string of assassinations targeting their fighters, a monitor said Friday.

“The Islamic State (ISIS) group has executed 16 men in Deir Ezzor and one more in Raqa, to send a message to all their opponents after recent assassinations of 12 Syrian, Iraqi and Algerian jihadists,” said Syrian Observatory for Human Rights director Rami Abdel Rahman.

“The men were accused of fighting ISIS,” Abdel Rahman told AFP, adding that only one of them had been proven to be linked to the assassinations.

He added: “ISIS is sending a message to all people living under its control, to say: ‘This is what will happen to any opponent.'”

The group emerged in Syria’s war in 2013 and in June declared a “caliphate” in areas under its control straddling Syria and Iraq.

It has committed some of the war’s worst abuses, carrying out near-daily executions in areas in its grip.

Most of Raqqah and Deir Ezzor provinces are ISIS-controlled.

Among those executed in the past two days in oil-rich Deir Ezzor were five members of the Shaitat tribe, which launched a local rebellion last year against ISIS.

The jihadists quelled the revolt, killing more than 900 tribe members in response.

Syria’s war has killed more than 200,000 people in nearly four years.

AFP contributed to this report.