UNITED NATIONS — The United Nations and American authorities are investigating a case in which a sizable amount of suspected counterfeit $100 bills was kept in a U.N. agency’s safe in Pyongyang for 12 years, and is yet to be turned over to American authorities.

An official familiar with the U.N. Development Program’s rules of operation told The New York Sun yesterday that several details of the agency’s public version of the counterfeit story “don’t make any sense.”

The official, who would only speak on condition of anonymity, said other officials in the agency’s New York headquarters must have known about the suspect bills much earlier than this month, as they claim.

Rather than a case of neglect, the official said, it is quite possible that the UNDP avoided reporting about the existence of the counterfeit bills because it feared that if a scandal came out, its operation in North Korea would be suspended.

The UNDP, the principal U.N. agency in Pyongyang, has withdrawn the bulk of its staff from North Korea recently anyway, after American officials accused it of violating its own rules. The United Nations has announced that it will audit all aspects of its activities in the communist country, but the audit may take a long time, as it apparently has not yet begun its work in earnest.

A sum of $3,500 in counterfeit bills is now known to have been stored in the UNDP’s safe 12 years ago, and the money is only now “in the process” of being turned over to American authorities, according to the agency’s spokesman, David Morrison.

“We are looking into the counterfeit angle,” an American government official who spoke on condition of anonymity confirmed.

Mr. Morrison yesterday detailed the outline of the story, which was first reported by Claudia Rosett in the online edition of National Review.

In Mr. Morrison’s version, an Egyptian consultant who provided services to the UNDP in North Korea was the source of the 35 bills in American currency that landed in the agency’s safe “sometime in 1995.”

The suspect bills remained in that safe until, according to Mr. Morrison, “UNDP senior management became aware of this last month and immediately sought the advice of U.S. officials on how to proceed.” Currently, he added, the UNDP “is making arrangements to turn the bills over to the U.S. authorities.”

Mr. Morrison’s version contradicts several of his previous statements, including his insistence that “we don’t deal in cash” other than small amounts that are defined as “petty cash.”

There have been seven managers of the Pyongyang office since 1995, the UNDP official who spoke to the Sun yesterday noted. “Do you want to tell me that none of them noticed that $3,500 in cash is lying in the safe, that none of them asked where that forgotten sum came from, and that they never reported it to headquarters?”

The official added that according to the agency rules, a “safe report” has to be filed with UNDP headquarters once a year, detailing the contents of the agency’s safe. “How did that money stay in the safe for 12 years then?” he asked. “This story just doesn’t add up.”

According to Mr. Morrison, the suspected counterfeit money was received by the UNDP when the Egyptian consultant “sent” the bills to its office in Pyongyang. “His bank had refused to accept the bills and invalidated them,” he added. Mr. Morrison has not identified the Egyptian man.

The consultant “informed us that these were bills that he received at a bank in the Democratic People Republic of Korea when he cashed a check we had given him for his services,” Mr. Morrison said. “He did not provide anything to enable UNDP or the DPRK Foreign Trade Bank to confirm that those were, indeed, bills from that bank. The DPRK Foreign Trade Bank did not accept the notes.”