Merrill Lynch said on Friday it had discovered an irregularity in its London trading positions and the Financial Times reported that a Merrill trader had been suspended over a suspected $400 million loss.

In a statement, the U.S. bank said senior managers were focused on the issue and said risks surrounding possible losses are under control but did not provide any details.

During a recent evaluation of certain positions, we discovered an irregularity, the bank said.

The statement came as Irish regulators said they were investigating the mispricing of trades at Merrill's London branch, an issue that they said was raised with them on February 18. Merrill said it was helping regulators with the investigation.

The Financial Times said a London-based trader at the bank had been suspended after trades on Norwegian and Swedish currencies went wrong, with potential losses of $400 million.

If confirmed, the losses will cause more severe financial headaches for Bank of America , the vast banking and investment house that bought Merrill last September and has since incurred sustained losses.

As part of its investigation, Ireland's regulator said it was liaising with the financial authorities in Britain and the United States.

The UK Financial Services Authority had no comment.

Earlier on Friday, The New York Times reported that Bank of America was probing whether Merrill had delayed booking trading losses until hefty bonuses were approved and the buyout deal was sealed.

While large, a $400 million trading loss would be little by comparison with the 4.9 billion euros lost by Societe Generale trader Jerome Kerviel in 2007, or the $1.4 billion lost by Nick Leeson in 1995, which collapsed his bank Barings.

Merrill's net loss swelled to $15.84 billion in the fourth quarter of last year amid big write-downs and investment losses on collateralized debt obligations and a variety of other high-risk securities.

Bank of America's stock has sunk 75 percent since the deal closed on January 1. The largest U.S. bank by assets now faces many shareholder lawsuits over the acquisition.

In mid-January the bank received a government bailout to help it absorb losses on $118 billion of troubled assets. Since October it has accepted $45 billion of government aid.

New York Attorney General Andrew Cuomo is conducting a probe into $3.6 billion of executive bonuses awarded by Merrill just before the Bank of America deal was sealed.

(Additional reporting by Juan Lagorio in New York and Steve Slater in London, Editing by Gerald E. McCormick, John Wallace, Richard Chang)