A cyber-attack, similar to one that saw $81m (£56m) stolen from Bangladesh's central bank, has hit a second bank.
The warning about the second attack came from Swift, which oversees the financial messaging network that underpins global money transfers.
Swift said the target was a commercial bank but did not name the organisation or reveal if any cash had been taken.
The attack used techniques and tools resembling those used to steal cash from Bangladesh in February, it said.
Swift is used by about 11,000 financial institutions around the world to move large amounts of cash.
The attackers had a "deep and sophisticated knowledge of specific operational controls" at the targeted bank, and could have been aided in their theft by "malicious insiders", said Swift.
In both attacks the thieves sought to submit fraudulent messages to the Swift network to transfer large amounts of cash to accounts they controlled.