GENEVA (Reuters) - The head of the U.N. agency for HIV and AIDS is stepping down in June, six months before his term ends, after an independent panel said that his "defective leadership" tolerated "a culture of harassment, including sexual harassment, bullying, and abuse of power".

Michel Sidibe announced the decision on Thursday at the end of a three-day board meeting of UNAIDS that examined the panel's report, the agency said in a statement.

The four-member panel, in a 70-page report issued last Friday, said that a "patriarchal culture of favoritism and cronyism" had allowed "impunity and retaliation". Sidibe, a Malian national, has been executive director since 2009 of the Geneva-based agency which has some 670 staff worldwide.

"He informed the UNAIDS Board that its meeting in June 2019 would be his last Board meeting and he would complete his duties at the end of June 2019," said a UNAIDS statement on Thursday night.

Sidibe was quoted as saying in the UNAID statement: "I look forward to an inclusive, transparent and open dialogue and collaboration with staff in shaping a new UNAIDS."

"I will work to ensure a smooth transition and pledge to keep my focus on our staff and delivering results for the people we serve."

The United Nations has tried to increase transparency and strengthen how it deals with serious accusations in recent years after a string of sexual exploitation and abuse charges were made against U.N. peacekeepers in Central African Republic.

"The UNAIDS Secretariat is in crisis, a crisis which threatens its vital work," the panel report said, citing results of staff surveys that "painted a troubling picture of the UNAIDS organizational culture that cries out for urgent change."

UNAIDS said last month it had placed its country director for Nigeria on administrative leave following allegations of sexual harassment. That case is one of three under investigation, UNAIDS spokeswoman Sophie Barton-Knott said.

In February, Luiz Loures, UNAIDS deputy head, said he would not seek to renew his term in office, although the spokeswoman said at the time it was not reasonable to link his departure to a sexual harassment allegation that proved unsubstantiated.

(Reporting by Stephanie Nebehay)