Isis jihadists have planted mines around the ancient ruins in Syria's Palmyra, prompting fears for the Unesco World Heritage site.
Militants from Isis (Islamic State) have reportedly carpeted parts of the Roman amphitheatre with bombs and explosives, according to Maamoun Abdulkarim, Syria's antiquities chief.
It was not immediately clear whether the the mines had been lain in preparation for the ruins' destruction, or as a deterrent to forces loyal to Syrian President Bashar al-Assad. The militants seized the strategically important nearby modern town of Tadmur from government forces last month.
The British-based Syrian Observatory for Human Rights, which draws on a network of monitors inside the country, said yesterday that regime forces had brought reinforcements to the west of the city in recent days, possibly in preparation for a fresh assault on the city.
It also said they had launched air strikes over Tadmur in the past three days, killing at least 11 people.
A former resident still in contact with relatives inside the city said that masked jihadists had announced their intention to rig Palmyra with explosives, delivering the message to residents gathered in the main market square. "We will accelerate pressure on the regime, and push the international community to stop them from shelling civilians," one of the militants reportedly said.
Bebars al-Talawy, a Homs-based activist in contact with Tadmur residents, described the ancient ruins as lying "between the hammer and the anvil, one belonging to the regime, the other to Isis".
The destruction of Palmyra's 2000-year-old ruins would deal the heaviest blow to Syria's cultural heritage in a four-year war.
Palmyra has been looted by government forces, damaged in fighting, and a section of its north defensive wall was hit by a regime airstrike.
Tadmur's fall had prompted fears that the extremist group would seek to destroy Palmyra's Unesco world heritage-listed ruins, as it has done with similar sites elsewhere in Syria and Iraq. But they had apparently left it untouched to date, to curry favour with locals over whom the jihadists are now consolidating their rule.
Instead, the amphitheatre has been revived as a stage from which the jihadists are underscoring their reign of terror. In late May, local residents were invited to the site to watch the execution of 20 people accused of being regime supporters.