Billionaire investor Carl Icahn offered to underwrite a $6 billion loan to CIT Group Inc. on Monday, complaining that a proposed solution hammered out by the cash-strapped, century-old commercial lender and its largest creditors is too expensive and detrimental to CIT's smaller bondholders.

In a blistering letter to CIT's board dated Monday, Icahn — who refers to himself as CIT's largest creditor — said the company is "shamelessly" offering to sell certain large bondholders $6 billion of secured loans "well below their fair market value."

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