The jihadist Islamic State group has executed nearly 1,500 people in Syria in the five months since it declared the establishment of a “caliphate,” a monitoring group said Monday.

“The Syrian Observatory for Human Rights has documented the execution of 1,429 people since the IS announced its ‘caliphate’ in June,” the group’s director, Rami Abdel Rahman, said.

The majority of IS’s victims in Syria have been civilians, he said.

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“Of the total number of people beheaded or shot dead in mass killings by IS, 879 have been civilians, some 700 of them members of the Shaitat tribe.”

The Sunni Muslim Shaitat tribe, from the eastern province of Deir Ezzor, rose up against the jihadist group in mid-2014.

Another 63 of the dead were members of other rebel groups or the rival jihadist Al-Nusra Front, which has fought IS in the north and east, Abdel Rahman said.

“Another 483 were regime soldiers, while four others were IS members” accused of corruption or other alleged offenses, Abdel Rahman said.

IS has executed large numbers of troops loyal to President Bashar al-Assad in recent months, after capturing government positions in central and northern Syria.

Many have been beheaded and their bodies put on display in public squares, “in order to strike terror into civilians and into any group that might decide to fight it,” Abdel Rahman said.

“Another aim of the IS executions is to terrorize the international community, while attracting new jihadists into its ranks,” he told AFP.

IS controls large swathes of Syria and neighboring Iraq where it is widely feared for its brutal abuses.

Syrian activists believe the group is holding hundreds of people hostage.

IS emerged from Al-Qaeda affiliate Islamic State of Iraq (ISI), and announced its presence in Syria in April 2013.