NAMA headquarters in Dublin.

Calls are growing for a cross-border inquiry into the sale of NAMA’s Northern Ireland portfolio which has been dogged by controversy.

In 2014, U.S. investment giant Cerberus paid NAMA – the Republic’s bad bank – $1.6 billion (£1.2 billion) for the loan portfolio.

“Project Eagle” was the biggest ever property deal in Northern Ireland.

NAMA was set up in 2009 by the Irish government and is responsible for recovering the value of problematic loans made by Irish banks that came to light as a result of the financial crisis.

Over a year ago, £7 million linked to the Project Eagle sale was found in an Isle of Man bank account.

Last week, BBC Northern Ireland’s Spotlight program reported that businessman Frank Cushnahan was recorded accepting a £40,000 cash payment from a NAMA borrower - this at a time when Mr. Cushnahan was working for NAMA.

Mr. Cushnahan has denied any wrongdoing, while property developer John Miskelly, who made the payment in a hospital car park, said “payments made by me to any persons have been lawful.”

Sinn Féin has called for a cross-border inquiry into the controversy, a call that has been backed by Fianna Fáil leader Micheál Martin.

Taoiseach Enda Kenny said he watched the Spotlight program and “found it quite incredible.”

“Nothing surprises me at the kind of activities that take place in politics.

“In that sense I find it extraordinary to hear the audio reports of engagements and meetings between certain personnel,” he said.

Speaking to Kfm radio, the taoiseach added: “If I find our colleagues in government find that this is a case that has to be examined, then I won’t be opposed to that.

“If there are questions arising from the Public Accounts Committee engagement with NAMA, and they are due before them shortly, I’m not averse to taking action, but I need to know what it is I’m taking action on.”

Micheál Martin said there is a now a need for a commission of inquiry into the Project Eagle sale.

“We have to know the limitations to such an inquiry, but nonetheless some useful work could be done by it that would not impede or undermine other investigations,” he said.

The Project Eagle sale is currently being investigated by the UK’s National Crime Agency and the Securities and Exchange Commission in the U.S.

The FBI has also been made aware of questions and issues surrounding the sale.

Project Eagle is also under investigation by the Finance Committee at Stormont and is being examined by the Oireachtas Public Accounts Committee in Dublin.

The Comptroller and Auditor General report on the Project Eagle sale is due to be published this week and it is expected to find that Irish taxpayers lost out on hundreds of millions of euros.