Baghdad - ISIL fighters who smashed ancient statues in the Mosul Museum and drilled through 3,000-year-old stone figures have warned this is just the beginning of the destruction, according to an official in contact with Mosul.

"They told the people they will go next to Nimrud," another of the Assyrian palaces and the site of one of the richest finds of gold objects in history, said the official who asked not to be quoted by name.

Archaeologists around the world have watched in horror the images of ISIL fighters in Iraq's second oldest museum destroying statues with sledgehammers and power drills.

Iraqi museum officials confirmed the authenticity of the video.

"I still think it’s a nightmare - that I'll wake up and it's not true," says Lamia al-Gailani, a leading Iraqi archeologist based in London.

ISIL fighters have occupied the museum since they took over the city in June. But they had refrained from damaging the pieces, telling residents they were guarding the museum.

Fit of complacency

Gailani, who has devoted half a century to Iraqi archaeology, says she and others were lulled into complacency.

"They didn’t do anything - there was hardly any theft of antiquities and you felt 'good they’re not going to touch the antiquities'," she said.

Museum experts say the statues smashing as they were toppled to the ground included at least one plaster copy but the rest were original artefacts from sites including the Assyrian cities of Nineveh and Nimrud and the Greco-Roman site of Hatra, they said.

Hatra, on UNESCO's list of world heritage sites, is known to film-goers as the site of one of the scenes of the The Exorcist.

The statues of the winged bulls, known as lamassu, were considered protective spirits containing the qualities of the animals they depicted.

They were often placed at the entrances of palaces.

Similar statues

More than a dozen other similar statues removed from Assyrian palaces are in museums outside Iraq, including the Louvre and the British Museum as part of agreements made at the time with foreign excavations.

Those remaining in Nineveh and Nimrud have stood guard since the palaces were constructed almost 3,000 years ago as part of a powerful empire that stretched from the Mediterranean to present-day Iran.

Both sites - an essential part of world heritage - have been neglected since 1991, when Saddam Hussein's invasion of Kuwait led to a decade of crippling trade sanctions that entrenched the country's isolation.

After 2003, corrugated iron roofs were installed to try to protect some the remaining bas reliefs and statues from erosion.

Museum officials say the most valuable pieces from provincial museums, including Mosul, were transported to Baghdad in 1991 for safekeeping and have remained there since.

Most of the statues destroyed by ISIL had been bolted into their bases and were too heavy to move.