The destruction of the ancient Assyrian city of Nimrud by ISIS in Iraq constitutes a war crime, the UN's cultural body UNESCO said Friday. Iraqi officials said the militants on Thursday began to destroy the site, which covers an area spanning about 8 kilometers and contains numerous treasures, including royal tombs. "The deliberate destruction of cultural heritage is a war crime," dpa quoted UNESCO chief Irina Bokova as saying. The destruction prompted an international outcry. US Secretary of State John Kerry called the reported damage "deeply disturbing." "This crude attempt to erase the heritage of an ancient civilization will ultimately fail," he said. "No terrorist can rewrite history." The United States urges the parties to respect and protect cultural sites and for those who destroy them to be held accountable, he said. Nimrud, about 30 kilometers south-east of Mosul, was founded more than 3,000 years ago and is considered the second capital of the Assyrian Empire, one of the greatest powers of early Near Eastern antiquity.