Banking giant Citigroup has posted huge losses as the global credit crisis continues to hit US banks.

The firm, America's largest banking group, made a net loss of $5.11bn in the first quarter of 2008.

Write-downs on investments hit by the crisis in the American sub-prime mortgage market reached $12bn.

Chief executive Vikram Pandit said: "Our financial results reflect the continuation of the unprecedented market and credit environment and its impact on our historical risk positions.

"During the first quarter, valuations of our sub-prime related exposures in fixed income markets and leveraged finance assets have further declined and credit costs in our consumer lending businesses have increased."

Citigroup made a net loss of $9.8bn in the final three months of 2007.