After spending nearly five years at the helm of the world's largest financial services network Citigroup Inc, CEO Vikram S. Pandit abruptly resigned on Tuesday.

Without citing any reason, Citigroup announced that Pandit had resigned from the top job with immediate effect. The abrupt resignation surprised the financial world as the resignation came just a day after the company posted stronger-than-expected third-quarter earnings.

Pandit was quoted as saying, "Given the progress we have made in the last few years, I have concluded that now is the right time for someone else to take the helm at the Citigroup."

However, a person with the direct knowledge of the developments at the company said that Citigroup directors had ousted Pandit for allegedly mismanaging operations that led to setbacks with regulators and decreased the company's credibility with shareholders.

In March, regulators had rejected the company's plan to boost shareholder payouts.

The person, who was speaking on the condition of anonymity, added that cut of the company's credit rating by Moody's Investors Service, and the $2.9 billion writedown on the Smith Barney brokerage unit also prompted directors to oust Pandit.

Michael L Corbat, the head of the bank's European & Middle Eastern division, has been appointed as the new chief of Citigroup.