Tillerson made the assertion at a press conference held in Kuwait, where he is attending a high-level meeting between members of a USA -led coalition against the Daesh terrorist group.
After declaring victory of the Islamic state, who occupied a third of the country, last December, Iraqi officials says rebuilding the country from the destruction left behind will cost more than $88 billion, with housing a priority.
Iraq received billions of dollars in credit lines, loans, and investment from Turkey, Gulf Arab allies, Europe, and other countries, their representatives announced at an worldwide conference in Kuwait on Wednesday.
The Kuwaiti capital is hosting the second day of an worldwide conference aimed at raising funds for reconstructing Iraq, which is reeling from the Daesh terror group's campaign of death and destruction.
Other worldwide players participating in the conference have also pledged their support, with the European Union promising €400 million ($494 million) in investment and the U.S. extending its $3 billion credit line, but not promising any direct government aid.
Kuwait will give $US1 billion ($A1.4 billion) in loans and $US1 billion in direct investments, a stunning donation as only a generation ago Saddam Hussein invaded the small, oil-rich nation. "Iraq can not commence the mission of rebuilding itself without support". Saudi Arabia pledged $1.5 billion.
Iraqi Prime Minister Haider al-Abadi also told the meeting that his government had managed to repatriate half of the displaced.
Overall, Baghdad is seeking $88.2 billion in aid from donors.
United Nations Secretary General Antonio Guterres urged the global community to address the scope of devastation that the war in Iraq has caused, saying the UN is firmly committed to the reconstruction process in Baghdad, which he reiterated would be a "daunting task.to ensure a unified nation". Iraqi army soldiers and allied fighters then launched operations to eliminate Daesh and retake lost territory.