Syrian government aircraft have launched at least 15 strikes in and around the ancient city of Palmyra following its fall to the Islamic State group.

The Syrian Observatory for Human Rights says at least four civilians have been killed in the raids, which were the most intense since the jihadists overran the city on Thursday.

“Since this morning, government aircraft have carried out at least 15 air strikes in Palmyra and the areas around it,” Observatory director Rami Abdel Rahman said.

• Islamic State seizes Syrian town Palmyra

He said that dozens of people had also been wounded in Monday’s raids, and that ISIS was believed to have taken losses when a military security building was hit.

The strikes targeted several areas of the city, including some close to the city’s famed Greco-Roman ruins, a UNESCO world heritage site, he said.

A military source confirmed operations were under way in and around Palmyra.

“Military operations, including air raids, are ongoing in the area around Al-Suknah, Palmyra, the Arak and Al-Hail gas fields and all the roads leading to Palmyra,” he said.

“We are pursuing Daesh wherever they are,” he added, using the Arabic acronym for ISIS.

ISIS is accused of executing hundreds of people in and around Palmyra since it swept into the oasis city last week after a lightning advance across the desert from its stronghold in the Euphrates Valley to the east.

The Observatory said on Sunday that it had documented the executions of at least 217 people, among them 67 civilians, including 14 children.

Some of those killed had been beheaded, Abdel Rahman said, adding that the jihadists had also taken some 600 people prisoner.

Syrian state media said at least 400 civilians had been killed by ISIS in Palmyra, most of them women, children and old men.

The pro-government Al-Watan daily reported on Monday that the number of executions had risen to 450.