Shortly after Alexander Yakovlev submitted his resignation on Tuesday night, the Independent Inquiry Committee, which is probing claims of fraud in the oil-for-food programme, requested that his office be sealed.
UN deputy spokeswoman Marie Okabe said IIC investigators planned to come to the United Nations on Wednesday to inspect the office.
Yakovlev, 52, worked in the procurement department, which oversees the awarding of UN contracts.
He was accused of helping his son get a job with IHC Services, a New York-based company that describes itself as a supplier of "branded product and services providing a diverse range of high-quality capital equipment".
According to his resignation letter, Yakovlev resigned over the allegations and because he wanted to "protect the integrity, reputation and the interest of the organisation," Okabe said.
Paul Volcker is probing the
Yakovlev was thrust into the public eye in February when he was mentioned in a report by the Independent Inquiry Committee, led by former US Federal Reserve chairman Paul Volcker.
There was no evidence that IHC did business under oil-for-food, the $67 billion operation that was aimed at helping ordinary Iraqis suffering under UN sanctions imposed after Saddam Hussein's 1990 invasion of Kuwait.
It has become the target of several corruption investigations since the Iraqi leader was ousted.
The inquiry committee largely portrayed Yakovlev as an employee who played strictly by the rules despite strong political pressure.
Some of his testimony was used as evidence against a colleague named Joseph Stephanides, who was fired by the UN on 1 June for manipulating contracts under oil-for-food.
Volcker spokesman Mike Holtzman said Yakovlev was still under investigation in the probe and that the request to seal his office was unrelated to the conflict-of-interest claims against him.
The UN received the allegations of a conflict of interest last week, and the UN investigative arm, the Office of Internal Oversight Services, is conducting its own investigation.
Okabe said the inquiry will continue and Yakovlev has promised to cooperate.