Hundreds of members of the Shueitat tribe in Syria have been shot and beheaded by the Islamic State, the militant group formerly known as the Islamic State of Iraq and Syria or ISIS, in the past two weeks, activists told the Associated Press Monday. The mass killings were committed because the Shueitat staged an uprising against IS rule in eastern Syria.

"They considered all members of the Shueitat tribe apostates because they rose against them," an unnamed activist told the AP. "Some men were taken out in the fields and beheaded them while others were shot in the head."

The exact number of Shueitats beheaded by IS was unclear. An activist based in Turkey told the AP as many as 200 members of the tribe were killed, while the Syrian Observatory for Human Rights, based in Britain, said 700 Shueitat tribe members were killed by militants.

Members of the tribe clashed with IS fighters for three days in eastern Syria, near the Iraq border, before IS launched a counteroffensive that led to the deaths of dozens of Shueitat tribe members.