After long consultations on perhaps the most prominent UN post across the globe, Annan picked 62-year-old Ashraf Jehangir Qazi to replace the UN envoy killed in a bombing in Baghdad last year, spokeswoman Marie Okabe said.

But she cautioned that it was unclear when Qazi would take up his post in the Iraqi capital due to the uncertain security situation on the ground more than a year after the US-led war toppled Saddam Hussein.

"Until circumstances permit security-wise, and we get the sufficient security guarantees from both the Iraqis and from the forces on the ground ... obviously these are considerations that will come into play before he can be deployed," she said.

The appointment of a highly respected Muslim, after weeks of internal haggling, reflected the importance the world body attaches to Iraq, where the United States reluctantly asked for help to stabilise a bloody insurgency.

Qazi replaces Sergio Vieira de Mello, one of 22 people killed in a bomb attack on the UN's Baghdad headquarters last year, which prompted Annan to withdraw all international UN staff from Iraq.