The United States expects to raise more than $2 billion this week for war-torn Iraq during a pledging conference in Washington, a senior State Department official said on Monday.

"We're hoping to raise in excess of $2 billion in what has been a roughly six-and-a-half-week pledging effort," the official told reporters ahead of the main pledge session for donor countries on Wednesday.

The Iraq donor meeting of 24 countries is being co-hosted by the United States, Canada, Germany, Japan, Kuwait and the Netherlands.

A broader meeting on a US-led campaign to fight Islamic State militants will be held on Thursday.

The conference is seeking to raise fresh funds to help Iraqi communities get back on their feet once their towns have been recaptured from Islamic State, as well as assist with the clearing of unexploded munitions preventing people from returning home, the official said.

The funds will mainly help deal with Iraq's humanitarian crisis, where more than 3.3 million people have been displaced by conflict, the official added.

The United Nations has estimated that Iraq needs a total of $4.5 billion in humanitarian assistance. That is far more than the $778 million that is currently set by the U.N.-led humanitarian response plan for Iraq, according to US and other officials.

Separately, the United Nations said in Geneva on Monday it needed $284 million in aid to prepare for humanitarian needs from an expected Iraqi assault on the Islamic State stronghold of Mosul. An estimated $1.8 billion would be needed to deal with the aftermath, it added.

Iraqi Prime Minister Haider al-Abadi has pledged to retake Mosul, Islamic State's de facto Iraqi capital, by the end of the year. – Reuters