Islamic State blows up prisoners tied to ancient pillars

Rome: Militants from the so-called Islamic State killed three captives in Syria by tying them to Roman-era columns in the ancient city of Palmyra and blowing them up.

The Britain-based Syrian Observatory for Human Rights cited activists as saying the executions took place on Tuesday at the Palmyra archaeological site which was captured by IS on May 20.

The identities of the three prisoners remain unknown, the monitoring group said. 

Since it overran Palmyra, the Islamic State has reportedly executed prisoners by firing and has destroyed ancient temples and other relics at the UNESCO World Heritage site. 

IS is known for its gruesome killings, including beheading and burning people alive. 

In recent months, the group has invented new execution methods, including crushing a soldier with a tank, according to the Syrian Observatory for Human Rights. 

The watchdog relies for its information on a network of activists and doctors inside Syria.