Merrill Lynch is expected to announce another huge asset write-down tomorrow, as the turmoil in the financial world continues to cost the world's biggest banks billions of dollars.

According to the Wall Street Journal, the US bank will report up to $8bn (£4bn) in new losses on securities backed by US mortgages – taking its total write-downs to about $30bn.

This would see the firm post a loss for the third quarter in a row for the first time in its history and could undermine chief executive John Thain's efforts to rescue the firm's fortunes.

The WSJ claimed the bank would also cut 10-15% of jobs in certain areas, including bond financing.

JP Morgan and Citigroup are also expected to announce fresh write-downs alongside their financial results this week, adding to the pain already caused by the credit crunch.

Merrill incurred its huge losses through its deep involvement in mortgage securities. It originally profited by packaging mortgages into complex vehicles such as collateralised debt obligations, but came unstuck when America's sub-prime mortgage market collapsed.

The resulting credit crunch has sent stock markets falling and sparked fears of tens of thousands of City job losses.

With consumer confidence also waning, prime minister Gordon Brown will meet with Wall Street bankers later today as part of his three-day visit to the US. He is expected to push for more action to fight the credit crunch.