Islamic State militants have placed mines throughout the UNESCO World Heritage site of Palmyra in Syria, an antiquities official and conflict monitor said Sunday, one month after the group entered the city.
The explosives were laid on Saturday, according to the Britain-based Syrian Observatory for Human Rights, which gathers information from sources inside the country.
"It is not known if the purpose is to blow up the ruins or to prevent regime forces from advancing into the town," Observatory director Rami Abdel Rahman told the French News Agency.
A museum at the site was emptied before the militants arrived in late May. The move was prompted by previous Islamic State attacks on artwork and artifacts during its campaign to establish a so-called "caliphate" across Syria and Iraq.
However, ruins from the ancient city, also known as Tadmur, could not be relocated.
In December, the U.N. said that during Syria's conflicts - which now includes violence from a civil war and the Islamic State group - more than 300 cultural heritage sites have been destroyed, damaged or looted.