DAMASCUS: ISIS militants have mined the spectacular ancient ruins in Syria’s Palmyra, an antiquities official and monitor said Sunday, prompting fears for the UNESCO World Heritage site.

The reports came one month after the extremist group overran the central Syrian city, known as Tadmur, and as government airstrikes were blamed for the death of at least 11 civilians over the weekend.

Syria’s antiquities chief Maamoun Abdel-Karim and the Syrian Observatory for Human Rights monitor said that the group had laid mines and explosives in Palmyra’s Greco-Roman ruins.

The Observatory, which relies on a network of sources on the ground, said the explosives were laid Saturday. “But 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 said.

He said regime forces had launched heavy airstrikes against the residential part of Tadmur, in the past three days, killing at least 11 people.

“The regime forces are to the west outside the city, and in recent days they have brought in reinforcements suggesting they may be planning an operation to retake it,” he added.

A political source said that a leading commander had been dispatched to the region to organize an offensive to recapture and secure Tadmur and several key gas fields nearby.

Abdel-Karim also said Sunday he had received reports from Tadmur residents that the ruins had been mined. “We have preliminary information from residents saying that this is correct, they have laid mines at the temple site,” he told AFP.

“I hope that these reports are not correct, but we are worried.”

He urged “Palmyra’s residents, tribal chiefs and religious and cultural figures to intervene to prevent this ... and prevent what happened in northern Iraq,” referring to ISIS’ destruction of heritage sites there.

“I am very pessimistic and feel sadness,” he added.

Last week, anti-regime activists accused the regime of conducting airstrikes that damaged the northern wall of one of the temple of Bel complex in Palmyra, and posted video footage purporting to show the aftermath of the strikes.

ISIS captured Tadmur, which is famed for its extensive and well-preserved ruins, on May 21. The group has regularly mined its territory to make it more difficult to recapture. The city’s fall prompted international concern about the fate of the heritage site described by UNESCO as of “outstanding universal value.”

Before it was overrun, the head of the U.N. cultural body urged that the ruins be spared, saying they were “an irreplaceable treasure for the Syrian people, and the world.”

ISIS has released several videos documenting its destruction of heritage sites in Iraq and Syria.

In its extreme interpretation of Islam, statues, idols and shrines amount to recognizing objects of worship other than God and must be destroyed.

There have been no reports of damage to sites in Palmyra since ISIS seized it, though the group’s fighters reportedly entered the city’s museum, which had largely been emptied of its collection before the militants arrived.

The group executed more than 200 people in and around Tadmur in the days after capturing the city, including 20 who were shot dead in the ancient ruins, according to the Observatory.

Before Syria’s war began, more than 150,000 tourists visited Tadmur each year, admiring its beautiful statues, more than 1,000 columns and formidable necropolis of over 500 tombs. It had already suffered before the arrival of ISIS, with clashes between rebels and government forces in 2013 leaving collapsed columns and statues in their wake.

The site is also believed to have been looted during the chaos of the war that began in March 2011 with anti-government protests.

In December, the U.N. said nearly 300 cultural heritage sites in Syria, including Palmyra, had been destroyed, damaged and looted.

Elsewhere, one person was killed and three wounded Sunday in a suicide bomb attack on the Kurdish-majority city of Qamishli in northeastern Syria, the official news agency SANA reported. “A terrorist detonated his explosive belt near the Hadaya hotel in the center of Qamishli, killing one person and seriously injuring three others,” the news agency said.

The Observatory said a member of ISIS had blown himself up at a Kurdish internal security forces headquarters, killing a member of the force and wounding 10 others.

The Britain-based monitoring group said the headquarters was located behind the Hadaya hotel, which serves as a government office.

Control of Qamishli is shared between Kurdish and Syrian government security forces.

The city has been spared much of the violence of Syria’s conflict, though it has on occasion been targeted in bomb attacks.

In March, 10 people, including five women, were killed in a similar ISIS attack against the Hadaya hotel.

In Idlib province, the Observatory said government airstrikes killed five civilians in the provincial capital and the town of Maaret al-Numan.