Banks have been warned of an imminent threat that their cash machines could be mass-hacked by cyber criminals.

In a confidential alert on Friday, America's Federal Bureau of Investigation told international banks that criminals are plotting a concerted global malware attack on cash machines in the next few days.

The FBI issued a warning about a highly choreographed fraud scheme known as an ATM "jackpotting", in which crooks hack a bank or payment card processor and use cloned cards at cash machines around the world to take out millions in just a few minutes.

UK-based banks with large international operations, such as HSBC and Barclays, are among those thought to have been made aware of the threat.

“The FBI has obtained unspecified reporting indicating cyber criminals are planning to conduct a global Automated Teller Machine (ATM) cash-out scheme in the coming days, likely associated with an unknown card issuer breach,” the FBI warning said, according to Krebs on Security, which originally reported the alert.