Secretary-General Kofi Annan (search) expects to quickly name a replacement for U.N. refugee chief Ruud Lubbers, who resigned as a controversy over allegations of sexual harassment escalated, the U.N. spokesman said.

Lubbers, who maintains the allegations are "made up" and "slander," said he would stay on as U.N. High Commissioner for Refugees (search) until a replacement is found.

U.N. spokesman Fred Eckhard said Annan told him on Tuesday that "he expects that this process will be transparent and rapid."

"I can't predict a specific date, but he'll be moving quickly," Eckhard said.

Traditionally, the top refugee post goes to a leading figure from a country that is a major contributor to the agency.

Allegations first surfaced last year that Lubbers had made unwanted sexual advances toward a female employee, identified in the media as an American. But it was only on Friday that the British newspaper The Independent published the first detailed description of her allegations and statements from four other women who didn't file official complaints but claimed Lubbers sexually harassed them.

With the United Nations (search) struggling to improve its image in the face of scandals over the U.N. oil-for-food program in Iraq and sexual abuse by U.N. peacekeepers in Congo, diplomats said Annan decided Lubbers had to go.

U.N. diplomats saw Lubbers' departure as part of a major effort to revamp the top U.N. leadership led by the secretary-general's new chief of staff, Mark Malloch Brown, whose primary job is to improve U.N. performance and overhaul its management.

Annan said Lubbers' resignation was in the best interests of UNHCR, its staff and the refugees it serves.

But UNHCR department heads wrote Annan expressing regret at Lubbers' resignation, saying that he should be remembered for "tireless determination" to help refugees and for creating an environment in which staff could express their views, "however divergent."

"We hope that all this, rather than the leaked investigation report of a complaint which you found could not be sustained, will be properly appreciated as the legacy of his time as high commissioner," they wrote in the letter, a copy of which was obtained by The Associated Press in Geneva.

Lubbers has volunteered his time and paid his own travel and expenses at the agency for the past four years.