Mosul Damn
The US government has warned of grave danger if the Mosul Damn is breachedGetty

A terrifying tsunami could kill hundreds of thousands of people in Iraq if the Mosul Dam suffered a "catastrophic" breach. The United States government warned there would be "severe loss of life, mass population displacement, and destruction of the majority of the infrastructure" if a wave "tens of feet high" was unleashed.

It has been under the control of Kurdish and Iraqi forces since August 2014 after US airstrikes helped seize the dam back off IS (Daesh), which assumed control earlier that month. It was feared the terror group would either cut off Mosul's supply to resources or destroy the structure to submerge residents.

"A catastrophic breach of Iraq's Mosul Dam would result in severe loss of life, mass population displacement, and destruction of the majority of the infrastructure within the path of the projected floodwave," a US government fact sheet said.

If the structure were to be destroyed, the wave would hurtle down the Tigris River toward Mosul before flooding major cities farther downstream, including the capital Baghdad. Iraqi Prime Minister Haider al-Abadi said there was no imminent threat to the dam but stressed people living near the Tigris River move to higher ground, at least 3.7m away from the river.

According to the United States, approximately 500,000 to 1.47 million people live along the Tigris in areas at highest risk and would probably not survive the impact of the projected flood wave unless they evacuated. "Proper preparation could save many lives," the embassy said.

The 3.2km-long dam – which was previously known as Saddam Dam – holds back as much as 12.5m cubic meters of water and is the largest in Iraq. Opened in 1984, it measures 113m tall and provides electricity to the 1.7 million residents of Mosul.

It will shortly undergo redevelopment funded by the World Bank with maintenance already under way.