Citigroup, the most profitable foreign bank in Taiwan, has completed acquisition of Bank of Overseas Chinese, boosting the US lender's number of branches on the island sixfold.

The transaction, announced eight months ago, cost the New York-based bank NT$13.9 billion (US$431 million), or NT$11.63 per share, Citigroup said in a statement on Saturday.

"This acquisition opens a new chapter for Citi in Taiwan," Robert Morse, chief executive officer of markets and banking for Citigroup in the Asia-Pacific region, said at a news conference in Taipei on Saturday. "It allows us to reach more clients across Taiwan."

Bloomberg News reported the takeover of Taipei-based Bank of Overseas Chinese bolstered the US lender's number of branches in Taiwan to 66 from 11, bringing access to one million additional customers.

Citigroup has also announced acquisitions in Japan and Chinese mainland as it competes with international banks including Standard Chartered Plc in Asia.