Chief Executive Stuart Gulliver told reporters the ultimate cost could be "significantly higher".
Several banks under investigation for suspected rigging of euro interest rates are cooperating with European Union antitrust regulators in the hope of lower fines, two people familiar with the matter told Reuters, a move which puts the lenders at a higher risk of lawsuits.
Italy auctioned 5.48 billion euros of bonds. The Rome-based Treasury priced the 10-year debt to yield 5.96 per cent, down from 6.19 per cent on June 28, and its 5-year bond to yield 5.29 per cent, compared with 5.84 per cent last month, according to Bloomberg.
Spanish bond yields also fell amid expectations the ECB will buy them to help ease the cost of borrowing.
"The main driver of Spanish and Italian bonds is the hope that we will see some concerted action" to help stem the debt crisis, Christopher Rieger, head of interest-rate strategy at Commerzbank in Frankfurt, told Bloomberg. "The risk is high that these hopes will be disappointed. We may not get all the details this week and so the market will probably remain volatile."
US Treasury Secretary Timothy Geithner and German Finance Minister Wolfgang Schaeuble met and backed a commitment by European leaders to do everything needed to defend the euro area while failing to mention its weakest link, Greece.
Wall Street, meanwhile, was even a little more cautious ahead of the Federal Open Market Committee's two-day meeting starting tomorrow.
In late afternoon trading in New York, the Dow Jones Industrial Average edged 0.04 per cent lower, the Standard & Poor's 500 Index fell 0.12 per cent, while the Nasdaq Composite Index shed 0.46 per cent.
One bright note: shares of Shaw Group soared 55 per cent after Chicago Bridge & Iron agreed to buy the company for about US$3 billion.