BAGHDAD (AFP) - The United Nations on Friday condemned as a "war crime" the bulldozing by the Islamic State group of the ancient city of Nimrud, the jihadists' latest demolition of Iraq's cultural treasures.

After rampaging through Mosul's museum with sledgehammers and torching its library last month, IS on Thursday "bulldozed" the nearby ruins of Nimrud, according to the tourism and antiquities ministry.

Antiquities officials said IS militants had moved trucks last week to the site, which overlooks the Tigris river, 30 kilometres (18 miles) southeast of their main hub of Mosul.

"Until now, we do not know to what extent it was destroyed," one official said on condition of anonymity.

Nimrud was the latest victim of what appears to be a systematic campaign by the jihadists to decimate Iraq's rich heritage.

"I'm really devastated. But it was just a matter of time, now we're waiting for the video. It's sad," said Abdulamir Hamdani, an Iraqi archaeologist from Stony Brook University in New York.

He said that the site's guards were denied access to Nimrud, which was founded in the 13th century BC and was once considered the jewel of the Assyrian era.

Its stunning reliefs and colossal statues of winged bulls with human heads guarding palace gates filled the world's museums in the 19th century.

A collection of 613 gold jewels, ornaments and precious stones found unearthed from a royal tomb in 1988 has been described as one of the greatest archaeological finds of the 20th century.

"Their plan is to destroy Iraqi heritage, one site at a time," said Hamdani.

"Hatra of course will be next," he added, referring to a 2,000-year-old UNESCO-listed site known for its beautifully preserved temples blending Hellenistic, Roman and Eastern influences.

Irina Bokova, the head of the UN's cultural body UNESCO, on Friday condemned the destruction of Nimrud "with the strongest force.”