"Local sources told us that 10 days ago Daesh destroyed the tetrapylon," a 16 columned structure that marked one end of the ancient city's colonnade, Maamoun Abdulkarim told AFP using an Arabic acronym for IS.
"Yesterday (Thursday), we received satellite photographs from our colleagues at Boston University showing damage to the facade of the Roman amphitheatre," he added.
Before being forced out of Palmyra in a Russian-backed offensive in March last year, IS carried out a campaign of destruction at the city's UNESCO-listed world heritage site, razing treasured temples and towers tombs.