A US investment firm that pulled out of buying NAMA's Northern Ireland loan portfolio over multimillion-pound fixer fees has accused the state agency of "repeatedly mischaracterising" its role in the controversy.

The Oireachtas Public Accounts Committee has heard Pimco ditched its bid to buy the so-called Project Eagle portfolio in March 2014 over concerns about £16m in "success fees".

The money was to be split equally between Frank Cushnahan, a former member of NAMA's Northern Ireland Advisory Committee, US law firm Brown Rudnick, and Ian Coulter, a managing partner of Tughans, a Belfast law firm subcontracted to assist in the deal.

In a letter read out by Committee Chairman Seán Fleming this morning, Pimco said it was "disappointed" that its withdrawal from the sale had been "repeatedly mischaracterised by NAMA".

"We would suggest that NAMA has conflated what may or may not have been discussed at the NAMA board level (upon which we can not comment) and the reality of the calls that Pimco made to NAMA and Pimco's own decision to withdraw," it said.

However, this afternoon NAMA rejected any suggestion that it did not set out the circumstances of Pimco's withdrawal accurately.

The investment firm said that at no stage did NAMA ask it to withdraw from the process, despite Pimco flagging concerns about the proposed fixer fees, which were never agreed, it added.

According to Pimco, NAMA said it was not aware of the fee arrangements but inquired if the firm would proceed with the sale should Mr Cushnahan's involvement or fee proposal be an issue for the agency.

"In no way did Pimco seek the acquiescence of NAMA to any fee arrangement nor sought agreement that any fee arrangement was appropriate," it said in a four-page letter, signed by Tom Rice, a chief legal officer at Pimco.

Pimco said it would not attend the committee hearings, which are investigating the controversial Project Eagle sale, because it did not want to prejudice investigations in the US and the UK.

The firm said it told NAMA just before pulling out of a proposed deal that it was disappointed disclosures had not been made by relevant parties to the agency.

It did not want to be part of any process "where there would be a suggestion of impropriety", it said.

Pimco added it was asked by NAMA if it had considered "other options" such as "proceeding without the three parties, and we were asked to consider before closing any doors whether every option was being considered".

The firm told NAMA on 12 March it had "no option but to withdraw" and NAMA expressed its disappointment but accepted the decision, the hearing was told.

The PAC is examining the Comptroller and Auditor General's report on the sale of the loans portfolio.

'PIMCO's withdrawal from Project Eagke repeatedly mischaracterised by NAMA'- says 'explosive letter'. @rtenews pic.twitter.com/ChsYySsr89 — Conor McMorrow (@ConorMcMorrow) November 10, 2016

This afternoon, a NAMA spokesman said that it has made its position clear to the PAC on the withdrawal of Pimco from the process.

The NAMA board was very clear that, if Pimco did not withdraw, then NAMA would exit them, the spokesman added.

He said that NAMA rejects any suggestion that it did not set out the circumstances of Pimco's withdrawal accurately.

The Project Eagle portfolio was eventually sold to US investment fund Cerberus for £1.2bn.

The C&AG found the sale incurred a potential loss to the taxpayer of £190m.

Brown Rudnick acted as advisers in the successful deal, which has been dogged by scandal for more than a year, including £7m linked to it being found in an Isle of Man bank account.

Mr Coulter resigned after it was unearthed.

Pimco said it was first approached about buying the portfolio by Brown Rudnick in April 2013, and the US law firm introduced Pimco to Mr Cushnahan and Mr Coulter.

The investment firm was told the Northern Ireland government wanted to ensure there would no fire-sale of the properties and that "it was a sensitive political matter and would have a major impact on the Northern Ireland economy".

Following a meeting with then first minister Peter Robinson and then finance minister Sammy Wilson in May 2013, Pimco was "informed by Brown Rudnick that it was the Northern Irish government's preferred purchaser for NAMA's Northern Ireland portfolio", according to the firm.

Members of the PAC have described the contents of the letter as "very serious" and "explosive".

Mr Fleming said a detailed response to the letter is needed from NAMA.

Sinn Féin's Mary Lou McDonald said the letter is "a game changer".

"It now seems that Project Eagle was conceived not by Pimco but by Brown Rudnick along with Tughans and Mr Frank Cushnahan," she said.

She accused NAMA of being "less than full in giving information over who knew what and when".

She said PAC focused on Mr Cushnahan and the fixer fees but this letter shows that he was "at the heart and the centre from the very beginning of this process".

She claims the letter shows that NAMA were aware of that.

Sinn Féin party colleague David Cullinane said: "I think it's fair to say that this is the most important piece of evidence that we have got.

"It is very illuminating and it joins up a lot of dots and it clearly contradicts evidence we got from NAMA. I think that is very worrying it. It casts doubt on the evidence presented to us by NAMA in respect of what happened when they were made aware of the success fees or fixer's fees."

Fianna Fáil TD Shane Cassells questioned the credibility of NAMA.

"The very core of this key evidence regarding Pimco shows that they (NAMA) has been dishonest with the committee."

Comptroller and Auditor General Seamus McCarthy has meanwhile told the hearing that he stands over his report into the sale of Project Eagle.