Iraq needs nearly $90 billion to rebuild after three years of war with the militant Islamic State (IS) group, officials said on Monday, with large parts of the country in ruins and tens of thousands left homeless.

As a three-day international reconstruction conference got underway in Kuwait, officials were seeking pledges from donors and investors to restore Iraq's devastated homes, schools, hospitals and economic infrastructure.

Baghdad declared victory against IS in December, after Iraqi forces, backed by a United States (US)-led coalition, regained control of the large parts of the country seized by IS in mid-2014.

Aid groups made pledges of $330 million on the first day of the conference, but officials said much more was needed.

Planning Minister Salman al-Jumaili said an assessment by Iraqi and international experts put reconstruction costs at $88.2 billion.

“The funds will be initially used to reintegrate displaced people and also for rebuilding the infrastructure of public services,” the minister told AFP.

Mustafa al-Hiti, the head of Iraq's reconstruction fund, said some work had started but that funds were needed urgently to restore basic infrastructure and services in many provinces.

“What we have accomplished is less than one per cent of what Iraq needs,” Hiti said.

“We have more than 138,000 houses damaged, more than half this number completely destroyed,” Hiti said, adding that more than 2.5 million Iraqis are still displaced.

After suffering a humiliating defeat at the hands of IS, Iraqi forces regrouped with foreign help, eventually forcing the militants out of territory including second city Mosul.

But the fightback left much of the country devastated. In Mosul entire city blocks were reduced to rubble.

'Unique opportunity' to help

The IS takeover also dealt a heavy blow to Iraq's economy.

The country sits on some of the world's largest crude reserves, which Baghdad puts at 153 billion barrels, but the war and a slump in world prices have diminished its oil revenues.

Raja Rehan Arshad of the World Bank said the investment is required across sectors, with more than $17.4 billion needed for housing alone. Nearly $30 billion is needed to restore energy and industrial infrastructure, he said.

The conference brings together hundreds of representatives of countries, aid groups, United Nations (UN) agencies and corporations.

The $330 million pledged by non-governmental organisations on Monday included $130 million from the International Committee of the Red Cross.

The UN refugee agency said the conference offered a “unique opportunity” to help displaced Iraqis rebuild their lives.

“Sustainable return is not just about bricks and mortar,” Bruno Geddo, UNHCR's representative in Iraq, said in a statement.

“Rebuilding and restoring communities is a complex effort, covering everything from clearing explosive hazards to repairing damage to infrastructure to restoring basic services, and facilitating social cohesion so that communities can again begin to flourish.”

UN agencies UNICEF and UN-Habitat called for urgent investment to restore basic infrastructure and services for children and families.

“Violence may have subsided in Iraq, but it has upended the lives of millions across the country, leaving one in four children in poverty and pushing families to extreme measures to survive,” they said in a joint statement.

The World Health Organization called for investment in hospitals and other medical facilities, pointing to more than 14 hospitals and 170 health facilities destroyed.

On Tuesday the conference will focus on private sector investment while on Wednesday national leaders are expected to announce governmental aid packages.

French Foreign Minister Jean-Yves Le Drian, whose country is a key member of the anti-IS coalition, visited Iraq on Monday ahead of attending the conference.

“I have come to tell you of France's support and to accompany you. We will always be there. We were there to participate in the coalition. We will also be there in the reconstruction phase,” Le Drian said after landing in Baghdad.