MOSUL DAM, Iraq-- A team of Italian specialists arrived Thursday at thesite of the Mosul Dam as part of an emergency campaign to repair Iraq's largest dam before it collapses.

The advance team from the Italian engineering firm Trevi Group will set up a camp for the group of engineers who are expected to arrive within a few weeks.

U.S. and Iraqi officials have repeatedly warned that the dam is in imminent danger of collapse.

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In late February, the U.S. embassy in Baghdad called the dam's risk of collapse "serious and unprecedented," and Prime Minister Haidar al-Abadi asked Mosul residents along the Tigris river to move at least 3.7 miles away from its banks.

The dam's core problem is that it was shoddily built on unstable ground: The earth underneath it is constantly being eroded by water. From the day it was inaugurated in 1985, maintenance crews have had to continuously pour cement under its foundation.

Without that constant injection -- known as "grouting" -- the 113-meter-high dam would soon collapse into a hole in the ground, causing an unprecedented disaster. The 30-mile long lake behind it would explode down the Tigris River valley with hundreds of millions of cubic meters of water, ramming into Iraq's second-largest city, Mosul, currently home to more than 700,000 people about 40 miles downriver. It would then flood all the way down to Baghdad, some 340 miles south.

U.S. officials have estimated more than a half million people could be killed. Millions more would be driven from their homes.

Things have worsened because the dam was captured for several weeks in 2014 by the Islamic State of Iraq and Syria (ISIS). U.S.-backed Iraqi forces retook the dam, but no grouting took place for six weeks. Even since then, the grouting has not been up to full levels in part because the militants control the nearby factory that produces the concrete for the dam.

As a result, there are "almost certainly ... an unprecedented level of untreated voids" in the dam's foundation from continuing erosion, the U.S. Army Corps of Engineers said in a Jan. 30 report.

Riyadh Izeddin, the dam's director, said that in addition to shoring up the dam's concrete, the engineers will also repair a faulty outlet gate, which allows water to be released from the reservoir and reduces pressure on the dam. The Italian crews will also be installing advanced technology and training Iraqi staffers on how to operate the new machinery.

CBS News' Holly Williams in March reported on ISIS fugitives and their life in Mosul under the terrifying rule of the extremist group.

People risked death to escape ISIS in Mosul, walking for miles through the night.

It's extraordinary when they escape, because very few people have managed to leave Mosul after ISIS began sealing it off -- stopping civilians from fleeing the city, and banning cell phones.

"These are torture marks," one man he said, showing scars on his back and arms. "They heated wire and used it to burn me."

His only crime was smoking, illegal under ISIS rule and its harsh interpretation of Islamic law.

Another man said he saw another Mosul resident beheaded after being caught with a cell phone sim card. One man told us three men were caught escaping recently, and ISIS hanged them in the street.

"They're a criminal gang," cried one man. "We've been surviving on water and bread."

"When they first came they were tough," said another. "But now they can see that Mosul is turning against them."

The men told CBS News they plan to fight against ISIS themselves now that they're free. They also want and to smuggle their wives and children out of Mosul as soon as they can.