Islamic State (ISIS) militants have attacked an ancient church in northern Iraq, tearing down the cross and relacing it with their flag, new images have revealed.

The images, which were released yesterday by an ISIS-affiliated Twitter account, show statues, murals and church bells being destroyed. One photograph shows a militant erecting a black ISIS flag in place of a cross on top of the Mar Gorgis (St George) monastery north of Mosul, a city entrenched in Christian history which was overrun by jihadists last June.

Militants are also shown destroying Christian paintings with hammers, while relics and a statue of Mary are thrown on the floor. The attack reportedly took place on March 7, though the images were published yesterday.

Last year there were reports that the monastery was being used by the jihadists as a female detention centre.

Before being overtaken by ISIS, Mosul was home to one of the world's oldest Christian communities. Members of the extremist Sunni Muslim faction drove Christians out of the historic city, forcing them to either flee, convert to Islam, or pay a tax. Those who refused risked death "by the sword".

ISIS has declared that ancient relics are idolatrous, and has destroyed many religious sites in Iraq and Syria. Earlier this month, militants bulldozed the ancient Assyrian cities of Nimrud and Hatra, both of which are UNESCO World Heritage sites.

Nineveh Yakou, an Assyrian archaeologist and director of cultural heritage and indigenous affairs at A Demand for Action, branded ISIS' actions "senseless", and told Christian Today that militants are "systematically targeting Iraqi heritage sites, in particular Assyrian sites, and I don't believe they will stop until Iraq has been levelled".

"This is not only a cultural heritage crisis. This is a humanitarian crisis of the highest state of emergency. ISIS are attempting to wipe out the people of Iraq and their history. This is an undeniable cultural and ethnic cleansing," Yakou said.