* Allegation not proven but official opts to go -UNAIDS
* Luiz Loures had over four-decade career fighting AIDS
* 40 sex misconduct allegations in U.N. in last part of 2017 (Adds age in 6th para, spokeswoman's comment in 8th para)
GENEVA, Feb 23 (Reuters) - The deputy head of the U.N. agency for HIV/AIDS will not seek to renew his term in office though it is not reasonable to link his departure to a sexual harassment allegation that proved unsubstantiated, a spokesman said on Friday.
Luiz Loures' exit was the second of a high-level United Nations official in as many days, after Justin Forsyth, deputy director of the U.N. Children's Fund, resigned saying he did not want coverage of his past mistakes to damage UNICEF.
Forty allegations of sexual exploitation and abuse were made during the last three months of 2017 against U.N. peacekeeping missions, agencies, funds and programmes as well as implementing partners, the United Nations said on Thursday.
A formal complaint of sexual harassment was brought against Loures in November 2016 but an inquiry found no basis for it, and the case was then closed, UNAIDS said earlier this month.
"The independent investigation done by the WHO's (World Health Organization) internal oversight services division clearly found that the case was unsubstantiated and recommended the case to be closed," spokesman Mahesh Mahalingam said.
Loures, 61, had had a long and distinguished career of four decades spent working on combating AIDS, including 22 years at UNAIDS, Mahalingam told a news briefing in Geneva.
"He clearly feels that this is time for him to move on." Mahalingam said it was not reasonable to link Loures' departure to the harassment allegations but that UNAIDS Executive Director Michel Sidibe had accepted the Brazilian national's decision not seek to renew his term, which expires at the end of March.
Mahalingam did not elaborate on the circumstances of Loures's departure. UNAIDS spokeswoman Sophie Barton-Knott, asked whether this had been negotiated, replied by email: "The decision not to request a renewal of his position was his own."
Tedros Adhanom Ghebreyesus, WHO director-general, asked about the UNAIDS case, told a news briefing on Feb 7: "On sexual harassment, I would like to assure you we have zero tolerance... (That) means we take the investigation very, very seriously."
Under U.N. rules, the decision to close the case may still be appealed to the administrative tribunal of the International Labour Organisation.
(Writing by Tom Miles and Stephanie Nebehay; editing by Mark Heinrich)
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