Elon Musk posted a video on Wednesday, claiming Tim Cook showed him around Apple's campus.
A reporter for The New York Times said on Twitter that Apple staff had spotted the two CEOs together.
Apple didn't respond to a request for comment; Musk's tweet comes after he slammed the company on Twitter.
Elon Musk claims to have met with Tim Cook at Apple's headquarters only two days after declaring "war" on the tech company.
Musk posted a video on Wednesday that appears to show the meditation pool at Apple's campus in Cupertino, California. New York Times reporter Kate Conger said on Twitter that Apple employees saw Musk and Cook together on campus on Wednesday.
"Thanks @tim_cook for taking me around Apple's beautiful HQ," Musk tweeted.
Spokespeople for Apple and Twitter did not respond to a request for comment from Insider ahead of publication. Musk didn't say in his video whether the apparent visit was from Wednesday - and he's been known to troll people on his social platform, though it's not clear if he was being serious about having met Cook.
If the meeting did happen, it came after Musk had some choice words for Apple and its CEO earlier in the week. Musk, who calls himself Twitter's "Chief Twit," on Monday accused Apple of exercising monopoly powers through its App Store. He also said the company opposed free speech.
"Apple has mostly stopped advertising on Twitter," Musk tweeted on Monday. "Do they hate free speech in America?
Musk later added that Apple had "threatened" to take Twitter off its App Store and "won't tell us why." He railed against the 30% cut Apple takes from in-app purchases made through apps on its iPhones. He even tweeted directly at Cook. The Apple CEO did not respond to Musk on Twitter.
If Apple decided to take Twitter off its App Store, it could present a significant hurdle to the social media company, slashing into user growth. Furthermore, Apple's 30% take could cut into Musk's plans to charge Twitter users $8 per month for verification.