At Baghdad's request, the United Nations Assistance Mission for Iraq (UNAMI) will shut down its operations after 22 years of assisting the country in its transition following the 2003 invasion and occupation that toppled longtime ruler Saddam Hussein.

"UNAMI was honoured and humbled to walk side-by-side with the Iraqi people," Guterres said at the mission's closing ceremony.

But "while a mission may conclude, the United Nations will always walk alongside the people of Iraq on the path toward peace, sustainable development and human rights," he added.

UN agencies and programmes will continue to operate in Iraq.

During a press conference earlier with Iraq's Prime Minister Mohammed Shia al-Sudani, Guterres said "there is one thing the world must understand, Iraq is now a normal country.

"Relations between the UN and Iraq will become normal relations with the end of UNAMI."

Sudani meanwhile said that the end of the UNAMI mandate "marks the beginning of a new chapter of cooperation".

"Our relationship with the United Nations through UNAMI was pivotal and effective in meeting Iraq's needs and supporting it until it reached the stage of full self-reliance," he added.

UNAMI was established by a UN Security Council resolution at the request of the Iraqi government before being expanded four years later.

Shortly after it was formed, a truck bomb struck the UN headquarters in Baghdad on August 19, 2003, killing the UN's first special representative in Iraq, Sergio Vieira de Mello, along with 21 others.

UNAMI's tasks included advising the government on political dialogue and reconciliation, as well as helping with elections and security sector reform.

But with Iraq regaining a sense of normalcy in recent years, authorities say there are no longer grounds for a UN political mission.