It's a battle of the tech billionaires.
Musk has repeatedly warned about the dangers of artificial intelligence, describing it as a potentially existential threat to the human race.
Zuckerberg has a different view. On Sunday, he responded to a question about Musk's warnings by saying he was tired of the fear-mongering.
"With AI especially, I'm really optimistic," Zuckerberg said during a Facebook Live broadcast. "I think that people who are naysayers and kind of try to drum up these doomsday scenarios -- I just, I don't understand it. I think it's really negative and in some ways I actually think it is pretty irresponsible."
Musk shot back on Tuesday morning with a tweet saying, "I've talked to Mark about this. His understanding of the subject is limited."
Musk added that a movie on the subject of AI was "coming soon," but didn't provide details about the film or his involvement.
Musk ignited a global discussion on the perils of AI in 2014. He predicted that humans might be doomed if we make machines that are smarter than us. But he said in a recent interview with the website waitbutwhy.com that his warnings haven't being heeded.
Musk, who's already leading space exploration projects and major tunneling initiatives, is now trying to develop AI that he hopes will have a positive impact on humanity. He's heading up a startup called Neuralink that intends to build devices to connect the human brain with computers.
Zuckerberg is no stranger to AI. He worked last year on developing an artificial intelligence system to help run his life and his home. After about 100 hours of work, he posted a video at the end of 2016 showcasing an AI system called Jarvis, which is voiced by the actor Morgan Freeman.
"My goal was to learn about the state of artificial intelligence," Zuckerberg said at the time, "where we're further along than people realize and where we're still a long ways off."
Facebook is also developing augmented reality features for smartphones and virtual reality worlds that can be experienced through the company's headset, Oculus.
Facebook CEO Mark Zuckerberg and Tesla CEO Elon Musk disagree over the dangers of AI.
In his Facebook Live broadcast on Sunday, Zuckerberg said that AI could be a force for good because it helps power self-driving cars and diagnose illnesses.
"If you're arguing against AI, then you're arguing against safer cars that aren't going to have accidents. And you're arguing against being able to better diagnose people when they're sick. I just don't see how, in good conscience, some people can do that. I'm just much more optimistic on this, in general, than probably a lot of folks are," Zuckerberg said.
Facebook and Tesla did not immediately respond to requests for comment on the feud.