Islamic State militants have sown landmines around ancient ruins in the Syrian city of Palmyra, captured by the Islamist group in May, according to a British-based monitoring group.

It wasn't clear, however, whether the move is a prelude to destroying the Roman-era sites or securing them from Syrian government forces, the Syrian Observatory for Human Rights says.

"They have planted it yesterday. They also planted some around the Roman theatre, we still do not know the real reason," Rami Abdulrahman, the head of the Observatory, told Reuters.

Maamoun Abdulkarim, Syria's head of antiquities, told Reuters that the reports of Islamic State planting bombs in Palmyra "seems true."

"The city is a hostage in their hands, the situation is dangerous," he told the news agency.

Since ISIS seized the city last month, there have been fears that the group would destroy the ancient city's historic treasures as happened in Mosul in February.

The BBC writes: "Government forces are reported to be planning a bid to recapture the site," quoting Abdulrahman as saying that Syrian soldiers outside the city had brought in reinforcements in recent days "suggesting they may be planning an operation."

"He said government forces had also launched heavy air strikes against the residential part of Palmyra in the past three days, killing at least 11 people."Copyright 2016 NPR. To see more, visit