During the past two weeks, the Islamic State militant group has executed 700 members of a tribe, many of them civilians, in eastern Syria.

The group, known as ISIS, had been battling members of the al-Sheitaat tribe, who have about 70,000 members. Many of the members were captured and beheaded by the militant group, reported Reuters.

“Those who were executed are all al-Sheitaat. Some were arrested, judged and killed,” said The Syrian Observatory for Human Rights director, Rami Abdelrahman.

Sheik Rafaa Aakla al-Raju, head of the al-Sheitaat tribe, appealed to other tribe members in a video posted on Sunday to join in the fight against the militant group. He warned that if the tribes do not band together, they would be “the next target” of the group.

According to the Daily Mail, about 300 men from the tribe were executed in one day. The remainder of those killed died in battle. Residents of al-Sheitaat tribal towns were given three days to leave.

Those who fled the towns traveled to Iraq or sought refuge in other villages.