Many, if not the majority, of the objects destroyed by Islamic State (IS) militants in a Mosul museum this week were modern plaster-cast reproductions of pieces held in other museums, British based experts told The Times of London on February 27.

Some originals of the pieces are held in other museums in Iraq or in the British Museum and other Western collections. The experts told The Times that the items that are in Western collections had been stolen during the 19th-century colonial era. One of the friezes shown being demolished in the video is a modern reproduction of an Assyrian piece whose original is in the British Museum in London, the experts said.

However, some of the objects smashed were priceless originals, including a set of huge, winged bull statues that had stood at the ancient entrance to Nineveh, the experts said. The statue depicted a 900 B.C. Assyrian protective god.

The video released by the Islamic State group on February 26 and which showed a group of militants smashing statues and other objects with sledgehammers caused outrage in Iraq and around the world. The video is thought to have been shot in the Mosul Museum and at Nergal Gate in Nineveh.

One of the militants explained that the statues depicted gods other than Allah and that they therefore had to be removed and destroyed.

"We do not care that we could have made millions of dollars," the militant said.

The Islamic State group has destroyed artifacts at hundreds of sites in Syria and Iraq. Reports this week said that the extremist group has ransacked Mosul's central library, burning more than 100,000 books and manuscripts.

Irina Bokova, the director-general of the UN's Educational, Scientific, and Cultural Organization (UNESCO) said earlier this month that the militants' actions constituted "one of the most devastating acts of destruction of library collections in human history."

Amid questions about whether the destroyed pieces were replicas or originals, The British Museum took the extraordinary step of announcing on its website that "We can confirm that none of the objects featured in this video are copies of originals at the British Museum."

"The British Museum is very concerned to see the reports that militants have destroyed items in the Mosul Museum and sculptures in the Nergal Gate Museum on the edge of Nineveh," the museum said. "We naturally deplore all such acts of vandalism and destruction of cultural heritage, and continue to monitor the situation to the best of our ability. In the absence of further information it is difficult to verify the details of those objects featured in the footage."

-- Joanna Paraszczuk