Archaeologists documenting Isil’s destruction of the ruins of the Tomb of the Prophet Jonah say they have made an unexpected discovery which could help in our understanding of the world’s first empire.

The Nebi Yunus shrine - containing what Muslims and Christians believe to be the tomb of Jonah, as he was known in the Bible, or Yunus in the Koran - was blown up by Islamic State of Iraq and the Levant (Isil) militants soon after they seized huge swathes of northern Iraq in 2014.

The shrine is situated on top of a hill in eastern Mosul called Nebi Yunus - one of two mounds that form part of the ancient Assyrian city of Nineveh.

The Iraqi army retook the area from Isil last month, revealing the extensive damage wrought by the jihadists.

But local archaeologists have told the Telegraph that Isil also dug tunnels deep under the demolished shrine and into a previously undiscovered and untouched 600BC palace.

Limited excavation was carried out by the Ottoman governor of Mosul in 1852, which was revisited by the Iraqi department of antiquities in the 1950s. But neither team reached as far as the palace.