Story highlights ISIS has horrified the world with the cruel methods in which it executes people

The Syrian Observatory for Human Rights reports of another heinous execution in the ancient city of Palmyra

ISIS has previously targeted treasured antiquities in the areas it controls

(CNN) ISIS, which comes up with more and more heinous methods of execution, has ramped up its cruelty: Members of the group tied three people to the pillars in the ancient section of Palmyra and killed them by detonating the pillars, the Syrian Observatory for Human Rights reported.

The group said it learned of the killings from local sources in the city, which has been under ISIS control since May. The London-based Syrian Observatory for Human Rights relies on activists inside Syria to document human rights violations in the country .

Not much else is known about the executions, including the names of the men or what they were accused of.

But ISIS has killed for the slightest of offenses and used brutal ways to do so.

In another recent execution, ISIS ran over a member of the Syrian military with a tank "because he ran over dead bodies of the Islamic State soldiers by tank."

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