Eliana Nabaa, a spokeswoman for the UN mission, said the man was kidnapped in the city of Baqouba, the capital of eastern Diyala province.
She added that Sunday's abduction took place near the government headquarters and that the UN is working with authorities to recover him.
A local security official said the man was grabbed from his car during the day. The victim's brother said the family has received a USD 100,000 ransom demand for the UN staffer's release.
Meanwhile today, eight bodies with gunshot wounds to their heads and chests were found in different parts of two Sunni-majority neighborhoods in western Baghdad, police said. Officers said they found no IDs with the bodies discovered in the Jihad and Ghazaliyah neighborhoods.
Dead bodies left in the street were a common occurrence during the widespread sectarian violence that engulfed Iraq several years ago.
All officials and the relative of the kidnapped UN staffer spoke on condition of anonymity because they are not authorized to speak to journalists or feared reprisal attacks.