American International Group (AIG) is under fresh pressure to reveal the names of the individuals who have not returned their bonuses as Connecticut’s Attorney General subpoenaed 14 current and former executives.

Richard Blumenthal expressed “deep concern and frustration” over AIG’s “lack of co-operation” in the investigation in a letter sent to the group's lawyers.

Andrew Cuomo, the New York Attorney General, is investigating whether or not AIG bonuses were paid fraudulently under New York law.

On Monday, some of the insurer’s more senior executives finally caved in to political pressure, with nine of the ten biggest bonus recipients agreeing to hand back the payments.

Mr Cuomo praised the AIG executives for having “risen to the occasion” and said that he hoped to recoup about half of the bonuses paid to them.

He added that he had not yet decided whether to release the names of the individuals who have not handed back their bonuses, as he weighed the security risk of such a disclosure.

Mr Blumenthal’s office did not name those executives who are being subpoenaed, but said that they would be required to testify at a hearing in Hartford, Connecticut, on Thursday.

It was unclear whether any AIG executives from the London office were being subpoenaed.

AIG’s bonuses have been the subject of intense public debate in the nine days since it emerged that, despite making the largest quarterly loss in corporate history of $61.7 billion, the company’s executives still received $165 million in bonuses for 2008.

The Connecticut Attorney General issued his subpoenas just hours after Ben Bernanke, chairman of the Federal Reserve, defended the US Government’s decision to rescue AIG with a $180 billion government bailout. “Its failure could have resulted in a 1930s-style global financial and economic meltdown, with catastrophic implications for production, income and jobs,” he said.

Timothy Geithner, the Treasury Secretary, called for new powers to take over and wind down failing financial companies after the government's troubled rescue of AIG.

“As we have seen with AIG, distress at large, interconnected, non-depositary financial institutions can pose systemic risks just as distress at banks can,” Mr Geithner said.

Mr Blumenthal has been doggedly pursing AIG about its bonuses. Having reviewed AIG’s financial documents, he disputes AIG's disclosure that it paid out $165 million in bonuses, saying instead that the figure was $218 million.

AIG has said that Mr Blumenthal's calculations are incorrect, although Mr Blumenthal is insisting that AIG's lawyers explain why his calculation differs from theirs.

Mr Blumenthal has described the AIG bonuses as “completely unjustified”. “These contracts rip the rug from under AIG's excuses - revealing no basis under Connecticut law for these mega taxpayer-funded bonuses. AIG's own documents reveal that it turned an emergency bailout into a meritless handout, paying windfalls to employees as reward for financial failure,” he said.

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