The announcement came moments after the US Federal Reserve announced new steps to ease access to emergency credit for struggling financial companies, by broadening the collateral to be used for central bank loans.

Lehman Brothers, the fourth-largest US investment bank, was on the brink of collapse on Sunday after talks with potential buyers hit a dead end.

Weekend talks with Britain's Barclays Bank and the United States' Bank of America faltered after the potential buyers said they were not convinced that Lehman, which last week announced a loss of $3.9bn in just three months, would be a good buy for shareholders.

Some analysts believe a Lehman collapse could trigger a shake up of the entire US financial system which has been stuck in the economic doldrums since the mortgage crisis hit more than a year ago.

"The US financial system is finding the tectonic plates underneath its foundation are shifting like they have never shifted before," Peter Kenny, managing director at Knight Equity Markets in New Jersey, said.

"It's a new financial world on the verge of a complete reorganisation."

The end of bidding for Lehman prompted a rare emergency trading session on Sunday which market sources said was initiated by the US Federal Reserve with the aim of reducing risk associated with a potential bankruptcy filing by Lehman, possibly on Monday.

The lack of a government guarantee to resolve the Lehman crisis is the main reason Barclays decided to exit the negotiations, according to a person familiar with the talks.

So far this year, the government has bailed out mortgage giants Freddie Mac and Fannie Mae, and saved Lehman rival Bear Stearns from going under by extending it cheap loans and allowing its forced sale to another rival, JPMorgan Chase.

Within hours of the collapsed Lehman talks, there were already reports of talks involving the takeover of Merrill Lynch & Co and the expected sale of assets by American International Group.

Over the weekend Alan Greenspan, the former US Federal Reserve chairman, projected the failure of "other major financial firms" but added that this did not need to be a problem.

"It depends on how it is handled and how the liquidations take place," he said on US broadcaster ABC.

"And indeed we shouldn't try to protect every single institution. The ordinary course of financial change has winners and losers."