Bond investors and regulators are stepping up their efforts to get others to pick up losses stemming from the mortgage meltdown.

In the latest round of score-settling, American International Group Inc. on Monday filed a lawsuit against Bank of America Corp. in New York Supreme Court. It is seeking to recover more than $10 billion on investments in mortgage-backed securities it initially purchased for about $28 billion between 2005 and 2007.

The 187-page lawsuit alleges "massive fraud" by Bank of America and two units it acquired, Merrill Lynch and Countrywide, saying that they packaged securities that were backed by "hundreds of thousands of defective mortgages." The lawsuit is one of the largest of its kind brought by a single investor since the housing bubble popped. AIG is likely to file similar suits against others, people familiar with the matter said.

Bank of America spokesman Lawrence DeRita said the bank's disclosures on the quality of mortgage bonds were robust enough for sophisticated investors. He called AIG "the very definition of an informed, seasoned investor" and said the insurer's losses were "solely attributable to its own excesses and errors."

Efforts to recover losses have picked up steam in recent months. In July, the federal regulator overseeing Fannie Mae and Freddie Mac filed a lawsuit against UBS AG , seeking to recover losses related to the sale of more than $4.5 billion in mortgage-backed securities. The lawsuit is expected to be the first of a number of actions filed by the Federal Housing Finance Administration.