GENEVA — Independent experts investigating allegations of sexual abuse at the United Nations agency fighting AIDS have called for the appointment of new leadership, saying in a damning report that its executive director tolerated harassment and bullying in a toxic organizational culture.

The agency, U.N.AIDS, was “in a state of crisis that threatens its vital work,” the expert panel said in its report, which was released Friday after a four-month investigation. The evidence of “a broken organizational culture is overwhelming,” it said.

The panel’s four members pinned responsibility for the crisis on the program’s executive director, Michel Sidibé, saying that under his autocratic leadership the agency had become a cult of personality marked by “favoritism, preferment and ethical blindness” that failed to prevent harassment and abuse or respond swiftly to accusations of ill treatment.

“A change in leadership has become necessary,” the experts concluded.

In an email to staff on Friday, Mr. Sidibé, a native of Mali who has led the agency since 2009, gave no indication of stepping down but instead mapped out a five-point plan for changes to be put into place next year.