The US Securities and Exchange Commission (SEC) has stepped up its scrutiny of the controversial sale of Nama's northern loan portfolio.
Belfast businessman Gareth Graham has travelled to the US to meet SEC officials after making corruption allegations to the financial watchdog, the Irish Independent understands.
The move came as Independent TD Mick Wallace made further allegations of corrupt payments linked to the Project Eagle deal.
Mr Wallace used Dáil privilege to claim a total of Stg£45m (€61m) had been "paid to fixers". The figure is in addition to more than Stg£7m (€9.5m) in an Isle of Man account Mr Wallace alleged was destined for a Northern politician or party.
It is understood Mr Graham passed documentation to the SEC several weeks ago.
His spokesman declined to comment.
Mr Graham told a Stormont inquiry earlier this month he was in possession of thousands of hours of taped phone calls involving former Nama adviser Frank Cushnahan. Although the tapes pre-date the Project Eagle sale by several years, Mr Graham said they showed an "ingrained culture of inappropriate and possibly illegal conduct" across political, banking, legal and accountancy sectors.
At the time, Mr Graham revealed he had held discussions with both the UK National Crime Agency and the SEC, which has the power to bring civil enforcement proceedings against companies engaged in fraudulent behaviour.
US vulture fund Cerberus, which bought the Project Eagle loans for €1.6bn (€2.2bn) last year, has denied making any improper payments. Mr Cushnahan has also denied any wrongdoing.
Speaking in the Dáil yesterday, Mr Wallace said that before Cerberus bought the portfolio, "individuals went around to big developers and asked whether they would buy their loans back for 50p in the pound".
Mr Wallace said the developers jumped at this proposal. "However, they had to pay a fixer's fee," he said.
"The Stg£7m in the Isle of Man... was only for openers. A total of Stg£45m has been paid to fixers."
Mr Wallace questioned how Cerberus could be under consideration as purchasers for Project Arrow, another loan portfolio Nama is currently selling, when it was "under criminal investigation".
In a statement, Nama said it had not been accused of, or involved in, any wrongdoing in respect of the Project Eagle sale.
"The ongoing inquiries in Northern Ireland relate to the alleged conduct of third parties on the buyer side of the Project Eagle transaction, and not to Nama," it said.
Meanwhile, two men named by loyalist figure Jamie Bryson as having been due to receive payments linked to the Project Eagle deal last night issued statements refuting his testimony. Developer Andrew Creighton said he did not claim, nor expect, to receive any payment in relation to Project Eagle, while accountant David Watters described the "unsupported testimony" as "completely false".