IS has carried out a sustained campaign of destruction against heritage sites in areas under its control in Syria and Iraq, and in mid-August beheaded the ancient city`s 82-year-old former antiquities chief.
The jihadists have already destroyed the shrine of Baal Shamin and the 2,000-year-old Temple of Bel, regarded as Palmyra`s masterpiece, since overrunning the citadel in May.
The Arch of Triumph, situated at the entrance of the ancient ruins` historic colonnaded street, was an "icon of Palmyra," Abdulkarim said, warning that IS fighters have already laid explosives in other monuments.
"This is a systematic destruction of the city. They want to raze it completely," he said.
"They want to destroy the amphitheatre, the colonnade. We now fear for the entire city," he added, calling on the international community to "find a way to save Palmyra."
Mohammad Hassan al-Homsi, an activist from Palmyra, backed up the account, saying: "The Arch of Triumph was pulverised. IS has destroyed it."
Sunni extremist group IS has destroyed pre-Islamic monuments, tombs and statues it considers idolatrous, but experts say they are also funding their "caliphate" by selling artifacts on the black market.
Both the citadel and the ruins are on the UNESCO World Heritage list, and before the war around 150,000 tourists a year visited Palmyra.
Activists said the city has also been damaged by heavy bombardment from barrel bombs dropped by Syrian government forces.
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