The group destroyed many priceless relics when it was previously in control of Palmyra, which dates back to the second century.
Islamic State militants have blown up part of the Roman amphitheatre in the ancient Syrian city of Palmyra, according to state media.
The SANA news agency said the facade of the amphitheatre had been destroyed together with the Tetrapylon, a four-sided Roman monument.
It did not give any more information about when the monuments were destroyed.
Maamoun Abdulkarim, the director-general of Syria’s antiquities and museums, said “We received satellite photographs from our colleagues at Boston University showing damage to the facade of the Roman amphitheatre.”
The United Nations cultural organisation UNESCO says the destruction of the historic site in Palmyra is a war crime, while a Kremlin spokesman described it as “a real tragedy”.
IS held the archaeological site for 10 months, destroying other monuments before being driven out by Russian-backed forces in March 2016.
Last May, Russia held a concert at the second-century amphitheatre to celebrate the victory.
But IS recaptured Palmyra in December as Russia forces switched their focus to the battle for Aleppo.
On Thursday the Palmyra monitoring group said IS had carried out a wave of executions in the ancient ruins of the city.
It claimed 12 people including teachers were murdered in front of a group of men and children,
They were either shot or had their throats cut, the group said. Other reports said they were beheaded.
“There are now fears that IS may carry out more executions of civilians who were arrested after it took control of the city,” it added.
“There are about 75 Palmyrene civilians still under arrest by IS and dozens of regime soldiers and militia men.”
IS have destroyed many ancient sites in Syria and Iraq, claiming the monuments support the worship of idols.