DES MOINES, Iowa - November 8, 2010 - Bond insurer Ambac Financial Group Inc. said Monday that it has filed for Chapter 11 bankruptcy protection after it failed to raise additional capital.

The embattled company also failed to arrange a structured bankruptcy agreement with senior debt holders.

It has tried for two years to regain its footing after getting pummeled by the collapse of the housing market.

The company continues to operate under the jurisdiction of the bankruptcy court.

As of June 30, it had $1.62 billion in debt. Assets were listed in bankruptcy court documents as $394.5 million.

The bankruptcy filing halts any debt claims. The company also is seeking a court declaration that would wipe out its tax liability for tax years 2003 through 2008 and that would allow it to keep the tax refunds it received for those years.

Documents were filed in the U.S. Bankruptcy Court for the Southern District of New York.

The Vanguard Group Inc. was listed as holding 5.46% of the company's stock, or 16.5 million shares.

The shares are spread across seven funds and no single fund owns more than 5 percent, documents said.