Tesla and SpaceX CEO Elon Musk called Facebook Chief Executive Mark Zuckerberg’s understanding of artificial intelligence (AI) “limited” Monday in an ongoing dispute between the two tech titans.

While responding to questions during a Facebook Live broadcast Sunday, Zuckerberg accused Musk of drumming up “doomsday scenarios” regarding the future of A.I.

“I think people who are naysayers and try to drum up these doomsday scenarios — I just, I don’t understand it,” Zuckerberg said. “It’s really negative and in some ways I actually think it is pretty irresponsible.”

“In the next five to 10 years, AI is going to deliver so many improvements in the quality of our lives.”

Musk responded online Monday after a Twitter user alerted the entrepreneur to Zuckerberg’s remarks.

I’ve talked to Mark about this. His understanding of the subject is limited.

— Elon Musk (@elonmusk) July 25, 2017

“I’ve talked to Mark about this,” Musk said. “His understanding of the subject is limited.”

Zuckerberg’s statement follows comments by Musk last week in which he called AI “a fundamental risk to the existence of civilization.”

Musk, speaking at the US National Governors Association summer meeting in Providence, Rhode Island, argued in support of preemptive regulation for the emerging technology.

“Normally the way regulations are set up is when a bunch of bad things happen, there’s a public outcry, and after many years a regulatory agency is set up to regulate that industry,” Musk said.

“It takes forever. That, in the past, has been bad but not something which represented a fundamental risk to the existence of civilization.”

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