The announcements are the latest from a lengthening queue of banks who have taken hits from a meltdown in U.S. subprime mortgages, which has set off a global liquidity crisis.

UBS said it would write down a net 4 billion Swiss francs ($3.4 billion) in its fixed-income portfolio and elsewhere, resulting in a third-quarter loss of 600 million to 800 million francs, its first quarterly loss in nine years.

UBS also said it would shed 1,500 jobs in its investment bank -- a sharp reversal of its recent buildup.

Citigroup, the world's largest bank by market value, said it was expecting a fall of about 60 percent in third-quarter net income.

Among the main culprits for the profit warning were $1.4 billion in pretax writedowns on funded and unfunded leveraged loan commitments.