WASHINGTON -- The International Monetary Fund (IMF) said in a statement late Wednesday night that its managing director Dominique Strauss-Kahn has resigned.

Strauss-Kahn denied the charges of sexual assault, attempted rape and unlawful imprisonment in his letter of resignation, saying that "I deny with the greatest possible firmness all of the allegations that have been made against me."

"I want to protect this institution which I have served with honor and devotion, and especially-especially-I want to devote all my strength, all my time, and all my energy to proving my innocence," he said in a formal letter of resignation informing the IMF Executive Board of his intention to resign as managing director with immediate effect.

The IMF will communicate in the near future on the Executive Board's process of selecting a new managing director. John Lipsky will remain as acting managing director before that, said the IMF.

Strauss-Kahn, 62, is under police custody after he was accused of sexually attacking a maid at the Sofitel New York hotel near Manhattan's Times Square.

"It is with infinite sadness that I feel compelled today to present to the Executive Board my resignation from my post of Managing Director of the IMF," he said.

"I think at this time first of my wife-whom I love more than anything-of my children, of my family, of my friends. I think also of my colleagues at the Fund; together we have accomplished such great things over the last three years and more," he noted in the letter.

The Washington-based agency said Wednesday that its acting chief John Lipsky has the authority to handle its regular business, in response to earlier comments from U.S. Treasury Secretary Timothy Geithner on the jailed Strauss-Kahn.

Geithner, responding to a question during a Tuesday event in New York, said Strauss-Kahn is "obviously not in the position to run the IMF."