American Express Co announced on Monday a new line of certificates of deposit as part of the largest U.S. credit card company's plan to diversify funding sources as the financial crisis tightened lending.

The saving lines, available in a range of maturities from three months to five years, will be insured by the Federal Deposit Insurance Corp (FDIC) by up to $250,000.

Unlike rivals such as JPMorgan Chase & Co , Bank of America Corp and Citigroup Inc , the company lacks of a strong retail deposit base to fund its operations.

American Express, like many credit card issuers, has funded itself through credit card asset-backed securities in recent years, but that market froze with the financial crisis.

Since then, the company has been increasing its offer of brokered deposits to try to fund at cheaper rates.

In the second quarter, 22 percent of the company's funding mix was from short-term debt, short-term and long-term retail deposits and institutional deposits. American Express has estimated those sources could represent up to 55 percent of its funding needs in coming years.

(Reporting by Juan Lagorio; editing by Andre Grenon)