Italian engineers hired to help prevent a catastrophic collapse of Iraq's largest hydro-electric dam will need at least two months to assess the structure before starting major maintenance work, a Water Resources Ministry spokesman told Reuters.

Mahdi Rasheed Mahdi said it might be six months before work begins on the Mosul dam as Italy's Trevi Group needed to bring in specialist equipment to plug gaps caused by erosion.

The dam, near the northern city of Mosul, was built in the 1980s on a friable gypsum layer on the Tigris and needs constant repairs to avoid disaster.

Maintenance work was disrupted for two weeks in August 2014 when the dam was captured by Islamic State militants seeking to carve a caliphate in captured territory in Iraq and Syria.

The dam's seizure prompted concerns that irreparable damage to the structure's foundations may have been caused. Collapse would devastate Mosul and other cities along the river, including the Iraqi capital Baghdad, and cause hundreds of thousands of casualties.

"They need two to six months and this was a request by the company," Mahdi said by telephone. "The company needs time to import their equipment and this definitely takes time. We have already anticipated this."

Mahdi said there was no imminent threat of collapse as some maintenance work was being carried out but more was needed to stabilise the structure. The Trevi contract would not provide a permanent solution, he added.

The dam was retaken by Kurdish Peshmerga fighters with the help of US-led coalition air strikes, and Iraq signed a 273 million euro (around $300 million), 18-month deal with Trevi to reinforce and maintain the 3.6-km-long (2.2 miles) structure.

Italy has said it planned to send 450 troops to protect the dam, which is close to the territory held by Islamic State fighters. – Reuters