Archaeologists and cultural officials have expressed heartbreak and outrage about the bulldozing of the ancient Assyrian city of Nimrud in Iraq.
Islamic State militants began demolishing the site on Thursday, Iraqi officials said.
The UN cultural body's Iraq director, Alex Plathe, called it "another appalling attack on Iraq's heritage".
"They are erasing our history," Iraqi archaeologist Dr Lamia al-Gailani told the BBC.
IS says ancient shrines and statues are "false idols" that have to be smashed.Nimrud, which was founded in the 13th Century BC, lies about 30km (18 miles) south-east of Mosul.
Many of the artefacts found there have been moved to museums in Baghdad and overseas, but larger artefacts remain on site.
'Levelled'
Nimrud covers a large area, and it is not yet clear whether it has been totally destroyed, says the BBC's Jim Muir in Beirut, neighbouring Lebanon.
But a local tribal source told Reuters news agency: "Islamic State members came to the Nimrud archaeological city and looted the valuables in it and then they proceeded to level the site to the ground.
"There used to be statues and walls as well as a castle that Islamic State has destroyed completely."
Last week, IS released a video apparently showing militants with sledgehammers destroying historic artefacts in a museum in Mosul.
That attack was condemned by the UN as a war crime.
Analysis: Vincent Dowd, BBC's arts correspondent
Nimrud is an ancient city on the banks of the River Tigris. In the Middle Assyrian period (the six centuries before 1,000 BC) it was known as Kalhu and appears in the Old Testament as Calah.
Assyrian power spread from northern Mesopotamia - the area now occupied by parts of Iraq, Syria and Turkey. For about 150 years Nimrud was the Assyrian cap
ital but eventually went into decline.
The first excavations in modern times were undertaken by Europeans starting in the 1840s. Treasures unearthed ranged from whole sections of royal palaces to individual statues and smaller artefacts.
For decades investigations stopped, but in 1949 Sir Max Mallowan (husband of writer Agatha Christie) began fresh excavations. He wrote the standard work, Nimrud and its Remains.
Other archaeologists later continued the work, especially from the 1970s when an extensive photographic record was made of the area's remaining treasures, some of which appear now to have been destroyed.
Source: BBC News
