The extent of the exposure - far bigger than the bank had led investors to expect - hit shares in its Swiss parent bank, Credit Suisse, which fell more than 10 per cent yesterday in Zurich.
The total Russian loss will almost certainly be far larger.
Some analysts said the figures suggested that the amount lost by CSFB in the Russian bond market, which has been the biggest source of red ink so far, would have been between $1.5bn and $2.8bn, depending on how CSFB valued the portfolio before the Russia crisis.
CSFB, which acquired BZW from Barclays last year, gave no further information on its bond losses, referring analysts to its statement last month which implied that its losses were closer to $400m to $500m.
The bank has also disclosed post-provision exposures to risky emerging markets, including Brazil and Korea, totalling more than $8bn. The significant exposures disclosed yesterday were:
South Korea: $2.37bn
Around $1bn of the Russian loans have been provisioned. The figures do not include equity exposure. CSFB accounts for a large slice of Credit Suisse's total earnings.
The Credit Suisse chief executive, Lukas Muhlemann, said yesterday that with total profits up 36 per cent to Sfr2.4bn (pounds 1bn) in the first half, the group had the financial strength to withstand further turbulence in emerging markets. CSFB alone reported a 32 per cent rise in profits to $4.4bn in the first half.
However, he admitted that the second half would be hit and that the group would not rule out a mega-merger if the right partner came along. "The Russian losses are well within the risk management limits," he said.
Credit Suisse has been under growing pressure to find a merger partner since UBS and Swiss Bank Corporation merged earlier this year. Speculation has centred on Deutsche Bank, whose head of investment banking, Josef Ackerman, is a former Credit Suisse executive.
Deutsche itself has been under pressure following the collapse of its investment banking operation and the recent loss of its coveted AAA debt rating on account of its own exposure to Russia and other emerging markets.
Credit Suisse has also suffered this year because of the adverse publicity connected with the Nazi Holocaust. The bank has taken a provision of Sfr375m in the first half to cover its share of the global settlement signed in August.
Mr Muhlemann said thatCFSB was not doing any new business in Russia. Most of the staff were working on trying to salvage existing positions.
He added that the amount of capital being committed to emerging markets business by the bank would be cut back.
Credit Suisse was by far the most heavily exposed of the large investment banks to Russia. Barclays has said it will be taking a pounds 250m provision because of the Russian crisis.
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