(DPA) -- German archaeologists have explored an ancient palace in Iraq that they could only access after the area was blown up by the Islamic State (IS) terrorist militia.

"The extremists caused a great deal of destruction, but we were able to gain insights because of it," Peter Miglus, Professor of Archaeology at the University of Heidelberg, said.

In the summer of 2014, IS supporters overran the city of Mosul in northern Iraq and later blew up a mosque on a hill above the grave of the biblical prophet Jonah. The mosque had been built over a military palace of the Assyrian Empire. After the blasting, the IS followers began to dig a system of several hundred metres of tunnels under the rubble, Miglus said.

When Iraqi security forces regained control of the city in 2017, the tunnels were preserved -- and with them access to the military palace.

At the Iraqi antiquities authority's request, researchers from the University of Heidelberg began to explore the site. The scientists discovered rare archaeological treasures in the tunnels. Inside the tunnel system, they came across the throne room of the military palace, which was once about 55 metres long. "The palace is partly well preserved," said Miglus.

Islamic State destroyed numerous archaeological remains during its rule over large areas of Iraq and Syria. South of Mosul, they blew up an approximately 3,000-year-old Assyrian palace in the former royal city of Nimrud. As elsewhere, they wanted to destroy everything they considered to be the places of "unbelievers". Above all, they reject any form of veneration of saints.