Islamic State militants have set explosives at the site of ancient ruins in Syria's city of Palmyra, which is also known as Tadmur.

According to the U.K-based Syrian Observatory for Human Rights, the explosives were said to be laid at the site of the Roman ruins in the ancient Semitic city, which is located in the central Homs province, on Saturday.

Government forces are reportedly preparing to recapture the site.

Rami Abdel Rahman, the director of the watch group, explained to reporters that Syrian soldiers outside the city brought in reinforcements in recent days, which leads him to believe that “they may be planning an operation."

Rahman said that regime forces launched heavy air strikes against the residential part of Palmyra in the past three days. This action has so far resulted in the deaths of at least 11 people, The Daily Mail reports. 

Maamoun Abdulkarim, Syria's head of antiquities, noted the veracity of the reports of Islamic State placing bombs in Palmyra, and said that “The city is a hostage in their hands, the situation is dangerous.”

In May, ISIS fighters captured the city of 50,000 people.

Palmyra is a UNESCO World Heritage site. Before the Syrian civil war, its ancient ruins typically attracted hundreds of thousands of visitors yearly.

"I hope that these reports are not correct, but we are worried," said Abdulkarim.

As reported in Fox News, Abdulkarim has called upon the people of Palmyra -- its residents, tribal chiefs, and religious and cultural figures -- to get involved in the effort to prevent the destruction of these ancient ruins.

"I am very pessimistic and feel sadness," said Abdulkarim.

ISIS has already destroyed a number of heritage sites and smashed ancient artifacts in museums in the countries of Iraq and Syria.