Citigroup Inc., the biggest American financial-services company, agreed to buy Prudential Plc’s Egg Internet banking unit for 575 million pounds ($1.1 billion), quadrupling its credit card customers in Britain.

Citigroup, which will pay for Egg in cash, will gain about 2.9 million cardholders in Britain, the New York-based company said yesterday in a statement. The purchase, Citigroup’s second in Britain in two months, will add to earnings in the first year.

Citigroup’s chief executive officer, Charles Prince, aims to produce at least 60% of profit overseas, up from almost 40% last year. He’s struck deals in Turkey, El Salvador, China, and Panama since the Federal Reserve lifted a ban on large takeovers by the bank in April. The sale marks a U-turn for Prudential’s CEO, Mark Tucker, who last year said he would return Egg to profit by integrating the bank with the company’s life insurance unit.

“It is a bit of a surprise given they have said Egg was a core business, but I think it makes perfect sense as Prudential is a life company and not a bank,” a London-based analyst at ING Financial Markets, Kevin Ryan, said.

Prudential shares fell 4.5 pence, or 0.6%, to 698 pence in London, valuing the company at 17.1 billion pounds. The stock is up 22% in the past 12 months, outpacing the 15% gain in the 29-member Bloomberg Europe 500 Insurance Index. Citigroup shares slipped 61 cents to $54.06 in New York.

In a separate deal today, New York-based Merrill Lynch & Co. agreed to buy First Republic Bank and its luxury-home mortgage business for $1.8 billion in cash and stock, the firm’s biggest acquisition in almost 10 years.