AMMAN (Reuters) - A prominent Iraqi Sunni politician on Monday warned Washington the acceleration in a military campaign in western Mosul to drive out Islamic State jihadists was causing a sudden surge in civilian casualties that threatened to undermine the effort to crush the militants.

Iraqi Sunni politician Khamis Khanjar speaks during his interview with Reuters reporter in Amman, Jordan, March 11, 2017. REUTERS/Muhammad Hamed

Khamis Khanjar, who has used his leverage to lobby the U.S. administration and the Iraqi authorities to ensure the major campaign in Mosul minimizes civilian losses among its population, said at least 3,500 civilians have been killed since the push into the western side of the side last month.

The army had earlier recaptured the east of the city in an offensive that began last year.

“There were heavy casualties due to speeding up of military operations and we see this as a big mistake and residents who we are in touch with have much more fear than in the past of the ongoing military operations,” Khanjar added in an interview in Amman.

“We hope the U.S. led coalition doesn’t hurry up in this way without taking into consideration the human lives,” he added.

Neither the Iraqi government nor the U.S. coalition have announced civilian casualties in the biggest ground operation in Iraq since the U.S led invasion of 2003.

Khanjar said the mounting casualties came mainly from air strikes and indiscriminate shelling of heavily crowded neighborhoods as the U.S trained elite Counter Terrorism Service (CTS) forces push deeper into the Old City and city center.

Fighting to drive Islamic State from western Mosul, its last major stronghold in Iraq, has involved close-quarter street battles, with Iraqi forces advancing block by block as they approach the most densely populated parts of the city.

Some 850,000 people are still believed to be living there, according to Khanjar.

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Until the latest phase of the battle to take western Mosul, the campaign had gone well with lower-than-expected civilian losses, Khanjar said crediting the professionalism of the U.S. trained elite forces.

“The Americans are mistaken if they think that a speedy decisive military solution is the best approach in this battle,” Khanjar added.

“This will have dangerous repercussions on the post-Mosul phase..there will be anger by residents and Daesh will benefit from the large human losses,” he added, using an Arabic acronym for Islamic State.

Khanjar is one of the main politicians in Iraq’s once dominant Sunni community and has spent millions of his vast fortune on a network of charities that helps supports thousands of displaced Sunnis whose areas have been battlefields.

He also financed local tribal Sunni groups that fought Islamic State when it first emerged in strength in Iraq.

At the outset of the Mosul campaign, Khanjar financed the 3,000 strong Turkish-trained force known as the Nineveh Guards Force that has now been integrated in state-run forces.

Iraq’s fractious Sunni senior politicians and parties also met last week in Ankara for the first time in years to chart a national reconciliation proposal in the post-Mosul period, Khanjar said.

In the meeting attended by Salim Jabouri, the head of parliament, Vice President Osama Nujaifi and other Sunni politicians, leaders agreed an historic opportunity existed to heal the rifts among Iraq’s warring sects and restore shattered confidence by mainstream Sunni toward the state, Khanjar said.

Deepening the disenchantment of Iraq’s Sunnis would only further alienate them and risk worsening the country’s security problems and even bring the emergence of even more hardline Sunni groups once the militants are defeated, he said.

“Unless there is a political process that restores confidence of Sunnis in the state..in a post-Daesh phase there may emerge more organizations of terrorists that are even more extreme than Daesh,” he said.

Mainstream Sunnis believe the Shi’ite led administration has discriminated against them and also say Shi’ite Iran’s influence has expanded in the security forces and paramilitary groups.