NEW YORK (Reuters) - John Thain, former chief executive of Merrill Lynch, has been ousted from Bank of America Corp., just three weeks after the companies merged.

Bank of America chief executive Kenneth Lewis expressed dismay last week about the scope of losses from mortgages and toxic debt on Merrill's books. Investors and analysts said the losses made Mr. Thain's position as head of global banking, securities and wealth management more tenuous.

"Ken Lewis flew to New York today, met with John Thain, and it was mutually agreed that his situation was not working out, and he would resign," Bank of America spokesman Robert Stickler said. The resignation is effective immediately. Mr. Thain could not be reached for comment immediately.

Bank of America shares fell 6.4 percent in afternoon trading.

Bank of America had threatened to back out of the merger, following the December 5 shareholder votes at both companies, but Lewis said regulators pressed him to complete the deal.

Last week, the government agreed to inject $20 billion in capital into Bank of America and to share in losses on $118 billion of debt.

Bank of America said Merrill lost $15.31 billion in the fourth quarter, separate from Bank of America's own $1.79 billion quarterly loss - its first in 17 years.

"This is a huge crisis of credibility," said David Dietze, chief investment officer at Point View Financial Services in Summit, New Jersey. "Someone has to fall on a sword."

Separately, CNBC reported the 53-year-old Mr. Thain had hired well-known Los Angeles interior designer Michael Smith to redecorate his Merrill office a year ago. CNBC said Thain ran up a bill of $1.22 million that included $35,115 for a "commode on legs" and $1,405 for a parchment waste can.

Mr. Smith's designing company could not be immediately reached for comment. The bank declined to confirm the report and Merrill representatives declined to comment.

Bank of America said the terms of Thain's departure would be disclosed later.

Mr. Thain's departure leaves Mr. Lewis without several top executives at Merrill, which it acquired on January 1 for $19.4 billion. Just a week ago, Mr. Lewis told investors he was happy that Thain was staying on. Other top Merrill executives to recently leave include Robert McCann, who was to lead the combined brokerage, and investment banking chief Greg Fleming.

The bank said Tom Montag, another former Merrill executive who took over Bank of America's sales, trading and research operations, is staying, contrary to a CNBC report he was leaving. Mr. Montag could not be reached for comment.

Lewis, who has spent some $130 billion on major mergers to build Bank of America, has raised the hackles of investors who believe the Merrill purchase was too many.

Pessimistic analysts have speculated the government may eventually need to nationalise one or more large banks if the global recession and credit crisis get worse.

Bank of America stock "is remarkably cheap by traditional measures," said Jack Ablin, chief investment officer of Harris Private Bank in Chicago. But he said, "The investment is still fraught with risk because of the potential for nationalization or the need for dilutive capital raising."

Shares of Bank of America were down 43 cents at $6.25 on the New York Stock Exchange, far below the 52-week high of $45.08 set last February 1.

Reports of Mr. Thain's office redecorating came on the heels of $12.2 billion in net losses at Merrill in the second half of 2007, as writedowns on mortgages and other toxic debt began to mount. Mr. Thain became Merrill CEO in December 2007.

The reported outlays recalled heavy spending on personal items by senior executives at other companies, including a $6,000 shower curtain owned by former Tyco International Ltd. chief Dennis Kozlowski, who is in prison for fraud and other charges.

Senator Richard Shelby of Alabama, the top Republican on the Senate Banking Committee, commenting on the report, said the office decorations would reflect "bad judgment" on Mr. Thain's part.

"I know John Thain and like him, but that was terrible precedent he set and a terrible decision," Mr. Shelby told reporters. "I wouldn't want my money spent that way."

Mr. Thain was considered a candidate to become US Treasury Secretary if US Sen. John McCain had defeated Barack Obama in the race for the White House.