The United States on Wednesday announced it was providing $181 million (160 million euros) in additional humanitarian assistance to Iraq ahead of an operation to retake the jihadist hub of Mosul.

The announcement was made by US Deputy Secretary of State Antony Blinken shortly after he arrived in Baghdad for meetings, including with Iraqi Prime Minister Haider al-Abadi.

"Today I am pleased to announce that the United States is providing more than $181 million in additional life-saving assistance to help meet critical humanitarian needs of those displaced by conflict, including those who will be affected as Mosul is liberated," he told reporters.

Blinken said the additional funding brought to around $1.1 billion the amount of humanitarian aid from the US to Iraq since 2014, when the Islamic State group took over parts of the country.

The United Nations has warned that an upcoming military operation on Mosul -- Iraq's second city and IS' last remaining major stronghold in the country -- could displace up to one million people.

"The new funding... will enable humanitarian workers to preposition emergency food supplies and basic relief items," Blinken said.

He said it would also provide for health care and education, as well as camp management, which was identified as a major flaw during the displacement that resulted from an operation to retake the city of Fallujah in June.

Blinken said Iraqi forces backed by the US-led coalition had retaken 50 percent of the territory IS held in Iraq two years ago and added that nearly a million displaced people had been able to return to their homes in liberated areas.

"Ultimately however, victory against Daesh (IS) on the battlefield is necessary but not sufficient to give citizens the confidence, the support and the services they need to return home," he said.

The aid community has said that aid appeals remain massively under-funded, leaving the country unprepared for what the UN has warned could be Iraq's biggest humanitarian crisis yet.

Abadi has promised Mosul would be retaken by the end of the year but the scope of the humanitarian needs and the difficulty of bringing all political forces together could make that deadline a hard one to meet.

Around 3.4 million Iraqis have been displaced since the start of 2014.