Bank of Montreal can double its U.S. customer base without further acquisitions by its Chicago-based BMO Harris Bank unit, Chief Executive Officer William Downe said.

Bank of Montreal has 600 branches serving about 3 million customers in the U.S. Midwest, Downe said Tuesday during a speech at the bank's annual investors' meeting in Toronto. U.S. personal and commercial banking is growing in step with, or ahead of, local markets, he said, and its existing BMO Harris Bank has the capacity to serve more customers and gain market share.

"With strong organic growth, we continue to believe we have the opportunity to double our U.S. customer base," Downe, 62, said.

Bank of Montreal, Canada's fourth-largest lender by assets, doubled its U.S. branches when it bought Marshall and Ilsley Corp. for C$4.1 billion ($3.2 billion) in July 2011, the biggest acquisition in its 197-year history. The bank last year earned more than 60 percent of annual profit from personal and commercial banking, with about a quarter of that from the U.S.

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