The Islamic State group's rampage through the ancient city of Nimrud in northern Iraq is an act of "cultural cleansing" that amounts to a war crime, and some of the site's large statues have already been trucked away for possible illicit trafficking, the head of the U.N.'s cultural agency said Friday.

In an interview with The Associated Press, UNESCO Director-General Irina Bokova described her angry reaction to Thursday's attack that came just a week after video showed Islamic State militants with sledgehammers destroying ancient artifacts at a museum in Mosul.

"We call this cultural cleansing because unfortunately, we see an acceleration of this destruction of heritage as deliberate warfare," Bokova said. She said the attack fit into a larger "appalling vision" of persecution of minorities in the region and declared that attacks on culture are now a security concern.

"It's not a luxury anymore," Bokova said.

The Iraqi government says Islamic State militants "bulldozed" the renowned archaeological site of the ancient city in northern Iraq with heavy military vehicles on Thursday.

Bokova said U.N. officials have to rely on satellite images of the destroyed city to assess the level of damage, because the dangerous security situation makes it impossible to get people close to the site.

But she said officials have seen images of some of the large statues from the site "put on big trucks and we don't know where they are, possibly for illicit trafficking."

Officials have seen photos of destroyed symbols of the ancient kingdom of Assyria, with the head of a human man and the body of a lion or eagle. She called them and other items at the site priceless.

"The symbolism of this, they are in some of the sacred texts even, in the Bible they are mentioned," she said. "All of this is an appalling and tragic act of human destruction."

She said that before the attack, UNESCO had been preparing to include Nimrud on its list of World Heritage Sites. The city was the second capital of Assyria, a kingdom that began around 900 B.C. and became a great regional power. The discovery of treasures in the city's royal tombs in the 1980s is considered one of the 20th century's most significant archaeological finds.

The site lies just south of Iraq's second largest city, Mosul, which was captured by the Islamic State group in June.

Bokova denounced the "cultural chaos" and said she had alerted both U.N. Secretary-General Ban Ki-moon and the prosecutor of the International Criminal Court.

She was meeting with Ban later Friday and described the U.N. chief's reaction to last week's destruction in Mosul as "rage." She said she was sure of his support.

She also said she plans to meet as well with Interpol, major museums such as the Metropolitan Museum of Art in New York, major auction houses and Iraq's neighbors in an attempt to stop the illicit trafficking of items from the Nimrud site.

Bokova appealed in a statement Friday to people around the world, especially young people, to protect "the heritage of the whole of humanity."

"I don't see any justification, any religious belief, any other kind of ambition, political or others, that justify this kind of destruction," she said.