Islamic State militants have just demolished the 2,000-year-old Arch of Triumph in the captured Syrian city Palmyra as the jihadist group continues its campaign to destroy heritage sites across Syria and Iraq, according to Syria's head of antiquities.

Maamoun Abdulkarim said his sources in Palmyra confirmed that the arch, a jewel in the exquisite collection of ruins in the oasis city, had been blown up on Sunday evening by the extremist group, Reuters reported.

"It's as though there is a curse that has befallen this city and I expect only news that will shock us. If the city remains in their hands the city is doomed," Abdulkarim told Reuters.

"It is now wanton destruction ... their acts of vengeance are no longer ideologically driven because they are now blowing up buildings with no religious meaning," he added.

The Arch of Triumph, situated at the entrance of the ancient ruins' historic colonnaded street, was one of the most recognisable sites in Palmyra that was known to Syrians as the "Bride of the Desert.'' It is the third major Roman-era architecture destroyed by the terrorist group since it took control of the city in May.

In August, the Sunni extremist group destroyed the first-century shrine of Baalshamin and another 2,000-year-old Temple of Bel, regarded as Palmyra's masterpiece, as part of its campaign to obliterate pre-Islamic monuments, tombs and statues it considers idolatrous.

It has also destroyed temples at the UNESCO World Heritage sites and buldozed other monuments and history building which it considers sacrilegious. It also plundered some of Palmyra's preserved funeral towers, sandstone constructions built to hold the remains of the ancient city's richest families, according to Reuters.

UNESCO has reportedly condemned the acts of the militant group, calling the destruction an "intolerable crime against civilisation.''

Abdulkarim, meanwhile, appealed to the international community to "find a way to save Palmyra" after the latest destruction.

He warned of an impending catastrophe in the UNESCO-listed world heritage site, which the jihadists have been dismantling since capturing the ruins in May, according to the Daily Mail.

"This is a systematic destruction of the city. They want to raze it completely,'' he told the Daily Mail. "They want to destroy the amphitheatre, the colonnade. We now fear for the entire city."

Since the Syrian civil war began four years ago, more than 900 monuments and archaeological sites have been looted, damaged or destroyed, according to Syria's archaeology association, the APSA.

Syrian government officials also said they have transferred some 300,000 artefacts to safe places in recent years, including from ISIS-controlled areas.