Syrian government forces launched at least 15 airstrikes in and around the city of Palmyra, according to a U.K.-based monitoring group. The raids came days after Islamic State group militants seized control of the ancient city in eastern Syria.

The airstrikes killed four people others and wounded others in Palmyra, according to the Syrian Observatory for Human Rights, an opponent of the regime of President Bashar Assad. The latest bloodshed adds to the city’s death toll in recent days, when the militant group formerly known as either ISIL or ISIS executed more than 200 civilians, the monitoring group said.

Palmyra’s 2,000-year-old Roman ruins are classified as a world heritage site by UNESCO, which describes the city as “one of the most important cultural centers of the ancient world.” The airstrikes Monday targeted parts of the city close to the ruins, the Telegraph in the U.K. reported.

Before Syria’s conflict began four years ago, more than 150,000 tourists visited the world heritage site annually.

The Islamic State group’s takeover of Palmyra has sparked concerns over the preservation of the ruins. This year, the militant group demolished pre-Islamic artifacts at a museum in Mosul, Iraq, and it destroyed parts of the ancient Assyrian city of Nimrud.

The Islamic State group achieved another major victory this month. Days before taking control of Palmyra, it defeated the Iraqi military at Ramadi, just 70 miles west of Baghdad. U.S. Defense Secretary Ashton Carter criticized Iraqi forces in unusually strong terms, saying they showed “no will to fight.”

More than 220,000 people have been killed in Syria’s conflict since March 2011.