(Reuters) – Maurice "Hank" Greenberg, the former AmericanInternational Group Inc. chief executive, has more than doubled thesize of his class-action lawsuit against the United States over theinsurer's bailout to roughly $55.5 billion from $25 billion.

In an amended complaint filed late Monday in the U.S. Court ofFederal Claims, Greenberg's Starr International Co said it is nowseeking damages over Maiden Lane III LLC, a vehicle designed to ridbanks of toxic debt underlying transactions with AIG.

The claims are in addition to claims that Starr previouslyasserted over the government's taking of a 79.9 percent stake inAIG in September 2008, which was eventually swapped for 562.9million common shares.

In the amended complaint, Starr said it is seeking to recover,on behalf of shareholders and the company, $23 billion over thegovernment's 79.9 percent stake, plus as much as $32.5 billion ofcollateral it said was given away through Maiden Lane III.

It is also seeking unspecified damages related to AIG's 1-for-20reverse stock split in June 2009.

Starr said the various actions constituted an illegal takingthat violated the 5th Amendment of the U.S. Constitution.

AIG in January refused to help Starr pursue the lawsuit, and onTuesday reaffirmed that refusal.

In an earlier version of the complaint, Starr estimated totaldamages as being "in no event less than $25 billion."

This phrase does not appear in the new complaint, which was alsofiled by Greenberg's lawyer David Boies of Boies, Schiller &Flexner LLP.

Prior to the bailout, Starr had held a 12 percent AIG stake,making it the largest shareholder of what had been the world'slargest insurer by market value.

A U.S. Department of Justice spokesman was not immediatelyavailable for comment. Robert Dwyer, a partner at Boies, Schiller& Flexner, declined to comment.

CLASS-ACTION LAWSUIT

Starr filed the amended complaint a few hours after U.S. ClaimsJudge Thomas Wheeler awarded class-action status to two groups ofshareholders, which the judge said could number in the tens ofthousands, challenging the $182.3 billion AIG bailout.

Maiden Lane III, named for the downtown Manhattan street whereAIG is based, was created by the Federal Reserve Bank of New Yorkto repurchase from AIG counterparties more than $62 billion ofassets linked to collateralized debt obligations.

Starr said the repurchases, sometimes done at 100 cents on thedollar, was a "backdoor" bailout for Goldman Sachs Group Inc ,Societe Generale SA and other banks that had entered more than $400billion of credit default swaps with AIG.

"Without any budgetary, regulatory, or other authority, FRBNYand its agents took or illegally exacted 79.9% equity and votinginterest from AIG in September 2008, (and) gave away AIG's legalrights and $32.5 billion of its collateral through the Maiden LaneIII transaction," the amended complaint said.

Starr is separately appealing the November 2012 dismissal of itsrelated lawsuit against the New York Fed.

U.S. District Judge Paul Engelmayer in Manhattan at the timesaid he found nothing to suggest that AIG directors were coercedinto accepting the bailout, which he called the result of"corporate desperation."

AIG OPPOSES GREENBERG

AIG decided on Jan. 9 not to join Greenberg's lawsuit, citingpotential harm to its reputation. Some politicians and voters hadrecoiled at the prospect that AIG might sue the same governmentthat had rescued it from collapse.

Starr attacked this decision, saying it stemmed from governmentcoercion and justified its lawsuit on AIG's behalf.

"The United States indicated it would wage a negative publicrelations campaign against AIG and its directors, terminate anycooperative relationship with AIG, and heavily scrutinize AIG'sSEC, tax, and other filings," Starr said in the complaint.

Jim Ankner, an AIG spokesman, said the board is standing by thedecision and opposes the lawsuit by Greenberg, who had led theinsurer for nearly four decades before his 2005 ouster.

"AIG will neither pursue these claims itself nor permit Starr topursue them in AIG's name," he said. "AIG will move to dismiss thederivative claims asserted by Starr in AIG's name."

On March 1, AIG eliminated the government's last financial stakeby repurchasing warrants from the Treasury Department.

The case is Starr International Co. v. U.S., U.S. Court ofFederal Claims, No. 11-00779.