Hundreds of millions of dollars are at stake as Bermuda-based bond insurer Assured Guaranty Ltd fights legal battles on two fronts.The UK unit of folded investment bank Lehman Brothers, which went bankrupt in September 2008, claims it’s owed more than $1 billion from an Assured subsidiary on derivative transactions.In a separate case, Assured is claiming that it was defrauded by JPMorgan Chase & Co’s EMC Mortgage unit in a $337 million mortgage-backed securities deal.Lehman Brothers International (Europe) sued AG Financial Products Inc in New York, saying the Assured unit improperly calculated termination payments under derivative deals.“We believe the claims by Lehman Brothers International (Europe) are without merit, and we will vigorously defend the lawsuit,” Ashweeta Durani, a spokeswoman for Assured, told Bloomberg News in an e-mailed statement.Lehman said in the complaint that “a proper calculation” shows AG Financial Products owes it more than $1 billion. AG Financial Products claimed it was owed $24.8 million from LBIE, according to the filing.In the other case, Assured has come forward with 36 new witnesses whom it says will back its claim that the bond insurer was defrauded by EMC.Lawyers for Assured filed a new complaint on November 18, unsealed this week, in a lawsuit accusing EMC and its parent at the time, Bear Stearns & Co, of misleading the bond insurer.The complaint, which also names JPMorgan as a defendant, includes a new fraud claim and new allegations from insiders at EMC and elsewhere.“The truth is now coming directly from Bear Stearns’ own former employees,” the insurer said in the complaint. “Seven confidential witnesses who were responsible for underwriting at EMC each have affirmed that they faced intense pressure to approve the purchase of high volumes of loans for Bear Stearns’ securitisations without adequate review.”Bear Stearns is a defendant in two other lawsuits in federal court in Manhattan by guarantors of mortgage-backed deals who say they were defrauded by the bank, which collapsed in 2008, according to the complaint. Assured Guaranty said its complaint adds to those suits by citing accounts from insiders and other sources.Jennifer Zuccarelli, a spokeswoman for New York-based JPMorgan, declined to comment on the new complaint.The suit focuses on a 2005 transaction known as SACO I Trust 2005-GP1, one of hundreds of securitisations by Bear Stearns from 2004 to early 2007. Assured Guaranty claims EMC knew that thousands of home-equity lines of credit that served as collateral for $337 million in securities it guaranteed were “junk” or otherwise flawed.