Senior London-based executives at American International Group (AIG) are among those understood to be holding out against returning their bonuses.

Andrew Cuomo, the New York attorney-general, is investigating whether AIG bonuses were paid fraudulently under New York law. His aides have confirmed to The Times that many, if not all, of those who have held on to their bonuses are based in London, where AIG’s financial products division has been held responsible for a large portion of the insurer’s spectacular losses.

AIG was under fresh pressure yesterday to reveal the names of the individuals who have not returned their bonuses after Richard Blumenthal, the Connecticut attorney-general, subpoenaed 14 present and former executives. Mr Blumenthal expressed “deep concern and frustration” over AIG’s “lack of cooperation” in his investigation into its compensation and bonus practices in a letter sent to the insurer’s lawyers.

His office did not name those executives being subpoenaed, but said that they would be required to testify at a hearing in Hartford, Connecticut, tomorrow.

On Monday, some of AIG’s more senior executives caved in to political pressure, with nine of the ten biggest bonus recipients agreeing to hand back the payments. Mr Cuomo praised them for having “risen to the occasion” and said that he hoped to recoup about half of the bonuses paid to AIG executives.

He added that he had not yet decided whether to release the names of individuals who have not complied, as he weighed the security risk of such a disclosure. However, a memo sent by an unidentified AIG executive and published byThe Wall Street Journallast night, appeared to advise employees in the company’s Financial Products division that their willingness to give back controversial bonuses would spare them from being publicly identified.

AIG’s bonuses have been the subject of intense public debate in the nine days since it emerged that, despite it having made the largest quarterly loss in corporate history – totalling $61.7 billion (£42 billion) – the insurer’s executives received $165 million in bonuses for 2008.

Mr Blumenthal issued his subpoenas hours after Ben Bernanke, Chairman of the US Federal Reserve, defended the Government’s decision to rescue AIG with a $180 billion bailout. “Its failure could have resulted in a 1930s-style global financial and economic meltdown,” he said.

Mr Blumenthal has been pursuing AIG. Having reviewed its financial documents, he disputes AIG’s claim that it paid $165 million in bonuses, saying it was $218 million. AIG has said that Mr Blumenthal’s calculations are incorrect. Describing the AIG bonuses as “completely unjustified”, Mr Blumenthal said there was no basis under Connecticut law for the mega taxpayer-funded bonuses.

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