Islamic State militants have destroyed parts of the second-century Roman amphitheater and an iconic monument known as the Tetrapylon in Syria's historic town of Palmyra, the government and experts said Friday.

It was the extremist group's latest attack on world heritage, an act that the U.N. cultural agency called a "war crime." A Syrian government official said he feared for the remaining antiquities in Palmyra, which IS recaptured last month.

Also on Friday, Turkey's military said IS killed five Turkish soldiers and wounded nine in a bomb attack in northern Syria.