The head of the Global Fund to Fight AIDS, Tuberculosis and Malaria on Wednesday said his decision to quit was triggered by a management reshuffle and cuts in spending plans.
Michel Kazatchkine was appointed the Fund's executive director in 2007 and had been reappointed for a three-year term in January 2011.
But on Tuesday, he announced he would step down on March 16 and the 10-year-old organisation said it was appointing Gabriel Jaramillo, a Brazilian former bank chief, as "general manager."
In an interview with the French radio station RTL, Kazatchkine elaborated on his decision to go.
"The reason is quite clear. The board took the decision to appoint a manager alongside me who would report directly to the board. As far as I am concerned, this is a question of principle. There cannot be two heads in an organisation," he said.
Kazatchkine also said he was "concerned (by) a certain number of reforms" that flowed from the Fund's failure to meet its money-raising targets last year.
"Donors, particularly the United States, asked us to reduce our funding estimates by 2.2 billion dollars over the next three years."
Kazatchkine angrily denied that he was quitting over a report in a French magazine, Marianne, which said the Fund had dished out money to Carla Bruni-Sarkozy, the wife of French President Nicolas Sarkozy, for an AIDS awareness project.
The report was denied by the Fund on January 6.
The Global Fund is the world's biggest single source of funding to tackle three of the world's greatest killer diseases, with a multi-billion-dollar budget drawn from more than 100 countries and private donors.
It provides grants for projects in developing nations, allocating money provided by governments and supporters such as the Bill and Melinda Gates Foundation.
The fund announced it was to beef up its financial safeguards in February last year after auditors found that $34 million (then 25 million euros) had gone missing or been siphoned off in four African countries, leading Germany to suspend its payments.
Source: AFP Global Edition