The United Nations' internal investigation unit has expanded a probe into allegations of sexual harassment by the U.N. high commissioner for refugees, according to the commissioner.

Ruud Lubbers, the former Dutch prime minister who heads the U.N. refugee agency, acknowledged May 18 that the U.N. Office of Internal Oversight had launched an investigation into allegations that he harassed a U.N. employee during a December meeting.

Lubbers, 65, wrote on Wednesday in an e-mail to his staff that the U.N. investigation team has decided "not to restrict itself to an investigation" into the woman's claim and that the investigators have begun questioning many U.N. staffers to determine if there was "a broader context."

"In plain words: could they not find other women who had somewhat comparable experience with me?"

The U.N. relief official also revealed that he had subsequently been accused of acting inappropriately with another woman who works at the refugee agency. "It was in no way sexual harassment, but I became aware at that time that she felt very uncomfortable," he wrote. "Therefore, I made an apology even in writing."

He indicated that he has no intention of resigning from his post and that he has appointed a "gender equality" specialist, Joyce Mends-Cole, to help establish new guidelines on sexual harassment.

Lubbers described his three-page note as a "frank report and apology" to his staff on the allegations and their impact on the agency's morale. But he also presented a vigorous assertion of his innocence, insisting that "there was no impropriety on my part."

And he sharply criticized U.N. investigators' handling of the probe, saying they have failed to contain leaks to the media, provide him a copy of the complaint or conclude the investigation in a timely fashion.

The director of the relief agency's office in New York, Eric Morris, declined to discuss the details of the letter or the investigation, saying only that Lubbers "was advised the investigation is underway and he thinks that the investigation should run its course."

The controversy represents a major distraction at the refugee agency, which cares for more than 20 million refugees in more than 120 countries. It has also exacted a personal toll on Lubbers, who is married and has three children.

"I am writing this on the eve of Pentecost," he wrote. "In this nightmare, there is certainly a personal dimension, but my main concern at this time if for the organization and you the staff."

Lubbers provided fresh details on the December incident, saying "I made what I consider, and I still consider to be a friendly gesture" to a female staffer as she left a Dec. 18 meeting on personnel matters with several other officials. He added that he "would have refrained" if he knew it would be considered inappropriate. "In short," he said, "I'm really sorry for that."

Lubbers said that the "misunderstanding may have been created or exacerbated by a joking reference" made to the woman outside the office by a colleague. "This appears to have given the friendly gesture a connotation of an entirely different nature than the one intended," he said. He also pointed out that the woman, whose name has not been made public, waited more than four months to file a formal complaint.