Barclays (NYSE: BCS) Chief Operating Officer Jerry del Missier resigned Tuesday amid the snowballing Libor-rate fixing scandal, joining CEO Bob Diamond and Chairman Marcus Agius to become the third senior leader at the world's fourth-largest bank to quit in just two days.

The resignation came as Barclays was preparing to demand that the American-born Diamond, 60, hand back almost £20 million ($31 million) in bonuses, according to Britain's Sky News.

It is understood that an estimated 12 more financial institutions are under investigation worldwide for Libor-related fraud.

Barclays Chairman Agius, 65, who announced his resignation on Monday, was widely seen as a sacrifice -- quickly proven futile -- to fend off calls for Diamond to resign.

It is understood the intense political pressure on Diamond -- once described as the unacceptable face of banking by former UK Minister Peter Mandelson  -- forced him to join the exodus at the top of the beleaguered lender and announce his resignation earlier on Tuesday.

A statement from Missier read: My 15 years at Barclays have been a time of great accomplishment, both for me personally and for the bank.

The firm is as strong today as it ever has been and is incredibly well placed to succeed within the post financial reform competitive landscape.

I have every confidence that the board and executive management of Barclays will be successful in executing their plans, and I wish them the best of luck in doing so.

Barclay's shares responded negatively to the latest resignations. By midmorning, its American Depositary Receipts had fallen 17 cents or nearly 2 percent to $10.60, a far cry from their 52-week high of $16.94.

The resignation of Diamond, one of the longest-serving executives at Barclays, marks merely the start of a whole host of challenges and legal issues to overcome.

The revolving door of senior management has caused more uncertainty surrounding the communication and organization of top executives.

It has been my privilege to serve as Barclays chairman for the past six years, Agius said Monday. This has been a period of unprecedented stress and turmoil for the banking industry in particular and for the wider world economy in general. Barclays has remained resilient throughout the crisis, and has worked hard to ensure that today it is a strong, well-capitalized and profitable business.

But last week's events -- evidencing as they do unacceptable standards of behavior within the bank -- have dealt a devastating blow to Barclays' reputation. As chairman, I am the ultimate guardian of the bank's reputation. Accordingly, the buck stops with me and I must acknowledge responsibility by standing aside, he added.

But the buck clearly did not stop with him.

In a surprise announcement posted on the bank's UK RSS feed and not on the bank's website, Diamond announced his own resignation and said Agius will become full-time chairman and will lead the search for a new chief executive.