WASHINGTON — The International Monetary Fund on Tuesday said the global credit crisis, despite some recent improvement, remains a significant threat to economic growth.

Even with "unprecedented intervention" by central banks such as the Federal Reserve, "financial markets remain under considerable strain, now compounded" by a slowing economy, low levels of capital at financial companies and widespread efforts to unload debt, the fund said.

The U.S. mortgage and credit crises could cause almost $1 trillion in financial losses, the IMF said in an update to its Global Financial Stability Report, with $565 billion of those losses stemming from the residential mortgage market and related securities, and the rest from the commercial real-estate, consumer-credit and corporate-debt markets.

That estimate is toward the higher end of estimates by many Wall Street economists, who have pegged the costs of the residential mortgage meltdown at $400 billion to $600 billion.

The IMF's figure includes $200 billion in losses that banks have already announced, plus an additional $80 billion the banks have yet to write down, IMF officials said during a briefing. The rest is held by other financial institutions, such as hedge funds and pension funds, the officials said.

"The deterioration in credit has moved up and across the credit spectrum to prime residential and commercial mortgage markets, and to corporate credit markets," said Jaime Caruana, director of the IMF's Monetary and Capital Markets department.

Credit markets have stabilized since last month, IMF officials said, when Bear Stearns Cos., the fifth-largest U.S. investment bank, was acquired by JPMorgan Chase & Co. at a fire-sale price.

But now, a weakening U.S. economy is placing "additional pressure on banks' balance sheets, which may limit their capacity to lend," Caruana said.

Caruana urged banks to seek additional capital so they can continue to lend and "avoid a credit contraction in the broader economy."

Caruana said investments earlier this year by government-run investment funds in large U.S. and European banks "have helped, but more may be needed to restore their lending capacity."

Government funds, also known as sovereign wealth funds, from China, Singapore and the Middle East invested more than $40 billion in Citigroup Inc., Merrill Lynch & Co. Inc., and Swiss bank UBS late last year and early this year.

The IMF is developing a voluntary code of best practices for the funds, which have sparked some concerns in the United States and Europe because they are government-run. Critics fear they could invest for noncommercial reasons, such as to obtain sensitive technologies.

Among other steps, the IMF recommended streamlining regulation of the financial sector to avoid subjecting banks and other financial firms to multiple supervisors.

Treasury Secretary Henry Paulson has proposed a regulatory overhaul along those lines that would eliminate some agencies and consolidate others. Most of Paulson's blueprint would require congressional approval, however, and is unlikely to be enacted before President Bush leaves office.