The visit - the first since last year's US-led invasion of Iraq - was aimed at ensuring that declared nuclear material already under International Atomic Energy Agency (IAEA) safeguards was not being used for undeclared activity.
IAEA spokesman Melissa Fleming said the visit had nothing to do with weapons inspections.
"WMD? It was not the purpose of their trip," she said.
Inspectors from the IAEA and the United Nations Monitoring Verification and Inspections Commission (UNMOVIC) left Iraq just before the US-led attack on the country in March last year.
Pretext for war
Although the war was fought under the pretext of unearthing and destroying Iraq's stockpile of weapons of mass destruction, no such weapons have been found and many analysts predict none will be found.
IAEA Director-General Muhammad al-Baradai said the mission was essential "to draft the final report on the absence of WMDs in Iraq so that the international community can lift the remaining sanctions on Iraq".
The IAEA and UNMOVIC were the two UN agencies charged with searching for WMDs in Iraq. The IAEA led the search for nuclear weapons while UNMOVIC looked for biological and chemical weapons.