Citigroup Inc (C.N) posted a quarterly loss to shareholders as it suffered $8 billion of credit losses, raising further questions about the future of the bank that is one-third owned by the U.S. government.

Citigroup, which has posted more than $100 billion of writedowns and consumer credit losses since the credit crisis began, posted a third-quarter net loss to shareholders of $3.2 billion, or 27 cents a share, compared with a loss of $2.9 billion, or 61 cents a share, in the third quarter last year.

Chief Executive Vikram Pandit has struggled to fix a bank formed through decades of acquisitions that resulted in a hodgepodge of fiefdoms. He has tried to shed bad assets and focus on Citi's main businesses, including international commercial and investment banking.

Some critics have accused Pandit of being slow to right the bank and deliver results. Citigroup has been bailed out three times by the U.S. government, including $45 billion of capital from the Troubled Asset Relief Program and a preferred share exchange that left taxpayers holding about a third of the company.

Pandit's relationship with regulators has been described by people inside the bank as sometimes contentious. But at a public event last month, Pandit said the bank was executing on its strategy, and as long as the company keeps executing, all the noise will disappear.

Citigroup shares fell about 25.5 percent between the beginning of the year and Wednesday's close. The KBW Bank index .BKX has risen about 11 percent during that period, and shares of Citigroup rival JPMorgan Chase & Co (JPM.N) have risen by about 50 percent.