Damascus, June 21 (IANS) The Islamic State (IS) militants have rigged the millennia-old city of Palmyra in central Syria with explosives, a monitor group reported on Sunday. The IS militants have planted mines and explosive devices in the ancient part of Palmyra, where 2,000-year-old monuments and temples are located, the Syrian Observatory for Human Rights said. It was **t immediately clear whether IS planted explosives to prevent the government troops from approaching, or to blow up the archaeological sites as they previously did in Iraq, according to the London-based group, which relies on a network of activists on ground.