The Iraqi government and the U.S. embassy in Baghdad are warning residents along the Tigris river of a possible collapse of the Mosul Dam. Iraqi Prime Minister Haider al-Abadi asked Mosul residents along the Tigris river to move at least six kilometers (3.7 miles) away from its banks in a statement released Sunday night.

In a similar statement also released Sunday, the U.S. embassy in Baghdad called the dam's risk of collapse "serious and unprecedented."

"Prompt evacuation offers the most effective tool to save lives of the hundreds of thousands of Iraqis," the U.S. embassy statement continued, estimating that floodwaters could kill nearly 1.5 million Iraqis living along the Tigris.

While U.S. officials have long issued warnings regarding Mosul Dam, the Sunday statements are the strongest public warnings to date.