The Islamic State jihadist group executed three people in Syria's ancient city of Palmyra by binding them to three historic columns and blowing them up, a monitoring group said.

Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said IS on Sunday "tied three individuals it had arrested from Palmyra and its outskirts to the columns... and executed them by blowing up" three columns.

Khaled al-Homsi, an activist from Palmyra, said IS had yet to inform local residents who the executed individuals were or why they had been killed.

"There was no one there to see (the execution). The columns were destroyed and IS has prevented anyone from heading to the site," Homsi, who works with the local Palmyra Coordination Committee activist group, told AFP.

Mohammad al-Ayed, also an activist from Palmyra, said the columns were "archeological, and there are many like them still present in Palmyra."

"IS is doing this for the media attention, so that IS can say that it is the most villainous, and so it can get people's attention," al-Ayed told AFP.

The Islamic State group has captured swathes of territory across Iraq and Syria to create a self-styled "caliphate" where it enforces an extreme form of Islamic rule.

IS considers pre-Islamic artefacts to be idolatrous and therefore worthy of destruction.

Since the jihadists seized Palmyra from regime forces in May, they have destroyed multiple sites and historic artefacts, including its celebrated temples of Bel and Baal Shamin as well as several funerary towers.

IS has used Palmyra's grand amphitheatre for a massacre in which child members of the group killed 25 Syrian soldiers, execution-style, in front of residents.

It also beheaded Palmyra's 82-year-old former antiquities director in August.

Palmyra's ruins are on the UNESCO World Heritage list, and before the war around 150,000 tourists a year visited the town.

Experts say the militants have used the destruction to raise their profile to attract new recruits, and are also funding their "caliphate" by selling treasures on the black market.

Syria's archaeology association, the APSA, says that more than 900 monuments and archeological sites have been looted, damaged or destroyed during the four-year civil war.