New York (CNN) — The head of the International Monetary Fund has resigned amid mounting calls he step down after being jailed on charges he sexually assaulted a maid in his upscale hotel suite in New York.

In a brief letter to the IMF executive board late Wednesday, Dominique Strauss-Kahn proclaimed his innocence.

He said he was stepping down 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.”

“To all, I want to say that I deny with the greatest possible firmness all of the allegations that have been made against me,” he said.