The head of the UN agency for Palestinian refugees has resigned amid an internal probe into alleged mismanagement and ethical abuses at the organization, the United Nations said Wednesday.

"A short while ago, UNRWA's Commissioner-General, Pierre Krahenbuhl, informed the secretary-general that he was resigning, effective immediately," UN spokesman Stephane Dujarric told a news briefing.

The UN earlier announced Krahenbuhl had been placed on administrative leave, to be replaced on an interim basis by the agency's acting deputy chief Christian Saunders.

An internal ethics report has alleged mismanagement and abuses of authority at the highest levels of the UN agency, which has also faced a financial crisis after the United States suspended and later cut all its funding for it in 2018.

UN investigators have been probing the allegations in the confidential report. The report describes "credible and corroborated" allegations of serious ethical abuses, including ones involving Krahenbuhl, a Swiss national.

According to the report, the allegations include senior management engaging in "sexual misconduct, nepotism, retaliation, discrimination and other abuses of authority, for personal gain, to suppress legitimate dissent, and to otherwise achieve their personal objectives."

Krahenbuhl himself was alleged to have been romantically involved with a colleague appointed in 2015 to a newly created role of senior adviser after an "extreme fast-track" process, the report says. That enabled her to join him on international business class flights, the report alleges. Krahenbuhl has rejected these accusations and said he would continue to reject.

"I can tell you clearly that there is no corruption case, nor fraud, nor mismanagement of funds received from donors," Krahenbuhl told Swiss television station RTS, adding that any personal relationship with a colleague "was confirmed as being non-existent by the internal report."

A number of other countries have suspended their contributions pending the outcome of the internal probe. Israel called the organization's operational model "unsustainable" quickly following the announcement of the probe.

"The international community needs to find a new model that will provide humanitarian assistance to those who truly need it, and must remove from the agenda the futile idea of the return of the refugees," Foreign Minister Israel Katz said in a statement.

UNRWA was set up in the years after more than 700,000 Palestinians were expelled or fled their lands during the 1948 war surrounding the creation of Israel.

It provides schooling and medical services to millions of impoverished refugees in Jordan, Lebanon and Syria as well as the Palestinian territories, and employs around 30,000 people, mostly Palestinians. 

A European diplomat speaking on condition of anonymity said he was "grateful for all (Krahenbuhl) did to stabilize the organization during a difficult time, but stepping aside now is the correct decision."

（With input from AFP)