The 116 experts are calling for a ban on the use of AI in managing weaponry.
"Once developed, they will permit armed conflict to be fought at a scale greater than ever, and at timescales faster than humans can comprehend," the letter says.
"These can be weapons of terror, weapons that despots and terrorists use against innocent populations, and weapons hacked to behave in undesirable ways," it adds.
There is an urgent tone to the message from the technology leaders, who warn that "we do not have long to act".
"Once this Pandora's box is opened, it will be hard to close."