Elon Musk has accused Mark Zuckerberg of failing to understand artificial intelligence.
It comes after the Facebook boss said that the doomsday scenario put forward by Mr Musk was unhelpful.
Mr Musk tweeted: "I've talked to Mark about this. His understanding of the subject is limited."
The pair represent two distinct groups, those saying AI's benefits will outweigh its negatives and those saying it could ultimately destroy humanity.
Mr Zuckerberg's comments were made as part of an informal Facebook Live chat, aired during a barbecue at his Palo Alto home.
A viewer asked him about a recent interview with Mr Musk, in which he said his biggest fear for the future was AI.
"I have pretty strong opinions on this. I am optimistic. I think you can build things and the world gets better. But with AI especially, I am really optimistic," Mr Zuckerberg replied.
"And I think people who are naysayers and try to drum up these doomsday scenarios - I just, I don't understand it.
"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."
Mr Musk began warning AI could destroy humans three years ago, when, during a talk at the Massachusetts Institute of Technology, the billionaire Space X founder called it humanity's "biggest existential threat".
And he has founded OpenAI, a billion-dollar non-profit company working for "safer artificial intelligence".
Bill Gates has also voiced concern about the threat AI poses, as has Prof Stephen Hawking.
But Mr Zuckerberg said: "AI is going to make our lives better."
And Facebook, the company he founded, uses AI to offer better targeted advertising, for curating news feeds and for photo tagging.