Mitsubishi UFJ Financial Group (MUFG) said on Wednesday that it has acquired a 72 percent stake in Thailand's Bank of Ayudhya Pcl for 170.6 billion baht ($5.31 billion) after concluding a tender offer last week.

MUFG, Japan's largest lender by assets, made an offer between Nov. 7 and Dec. 13 to buy up to 75 percent of Bank of Ayudhya for as much as 560 billion yen ($5.44 billion).

The deal will mark the biggest acquisition by a Japanese bank in Southeast Asia.

MUFG is planning to merge its existing Thai operations with the domestic lender to comply with Thailand's single presence policy on bank ownership. The acquisition and merger plan had surprised Japanese rivals, given that MUFG already had substantial operations with Japanese businesses in the country.

MUFG has the biggest overseas operations among Japan's banks. In 2008, it bought out UnionBanCal Corp, the holding company for California-based UnionBank, and paid $9 billion for a 20 percent stake in Morgan Stanley.

In 2010, it acquired a $6.4 billion project financing loan book from Royal Bank of Scotland.

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