Story highlights 13 children were among the victims

ISIS commonly executes opposing fighters and also civilians when it takes a city

(CNN) When ISIS captures a city, the bloodshed is hardly over, as the militants summarily execute captive fighters and residents by the dozens. In Syria, they have killed more than 250 of them in less than two weeks.

At least 13 of the victims were children, said the Syrian Observatory for Human Rights, a Syrian expat watch group.

As ISIS has taken control of the Syrian city of Palmyra in the last 10 days, it has executed 217 people there and in other towns caught in the military campaign, SOHR said.

Beheading preferred

Most of the victims, 150, were Syrian soldiers or allied militiamen -- or others who were accused of acting as their informers. Beheading was the preferred method of their execution.

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