BAGHDAD (AFP) - ISIS has released a video in which militants can be seen using rifles and sledgehammers to destroy artefacts at the ancient city of Hatra in Iraq.

Destruction at the Unesco World Heritage Site had already been confirmed by the United Nation's cultural agency a month ago.

The latest, undated video was released on April 3, a day after the ISIS group lost the city of Tikrit to government and allied forces, its biggest military setback yet in Iraq.

"The Islamic State has sent us to these idols to break them because they are worshipped instead of God," says one of two militants speaking to the camera.

"Some apostate organisations have said that destroying such antiquities is a war crime, so we will destroy them," he said.

The video shows ISIS (Islamic State in Iraq and Syria) militants knocking sculptures off the walls of a building, shooting at them with an assault rifle and hacking away at a statue with a pickaxe.

The destroyed artefacts as seen on the video have metal rebar inside them, leaving it unclear whether they are reconstructed originals or recent replicas.

Hatra is an extremely well-preserved city with a unique mix of eastern and western architecture, located in a desert area about 100km south-west of the northern extremist hub of Mosul.

The destruction there began around a month ago and came after ISIS militants also damaged the site of Iraq's ancient Assyrian city of Nimrud and destroyed dozens of pieces from the museum in Mosul.

Unesco has condemned ISIS' systematic campaign against Iraq's rich heritage as a war crime.

In a tweet posted after the release of the latest video, Unesco said: "We must stand up against forces that seek to divide Iraq. They attack the humanity we all share."