Bank of New York Co. said Monday that it had signed a contract to buy the global custody operations of Royal Bank of Scotland, solidifying an agreement announced by the two companies in March.

The deal includes $640 billion in custody assets in Royal Bank's RBS Trust Co. subsidiary. The companies said they still need regulatory approval but hope to close the deal by the end of September.

Terms were not disclosed. Royal Bank said in March that the transaction could fetch as much as $672 million, including an up-front payment and a payment over three years contingent on how many of Royal Bank's custody clients sign on with Bank of New York.

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