Speaking on Twitter, Musk suggested that World War III could begin if Russia loses Crimea, which holds military significance for Russia and was annexed from Ukraine in 2014.

Musk began the discussion of the war after retweeting a Newsweek op-ed by venture capitalist David Sacks.

Sacks, who revealed being a friend of Musk and investor in SpaceX in the article, defended the Tesla CEO for his online conversations about how peace between Russia and Ukraine could be reached.

At the beginning of October, Musk proposed that Crimea should remain under Russian control with an “assured” water supply and insisted that peace would depend on Ukraine remaining “neutral” about world affairs.

The tech billionaire also said recent referendums concerning the annexation of four regions of Ukraine—which the West dismissed as “sham” elections—should be redone with United Nations supervision. He argued that Russia should leave the regions only “if that is will of the people.”

Following his tweet of the op-ed, Musk was asked by a Twitter user whether he thought there was a possibility the Ukraine-Russia conflict could result in a nuclear war or World War III.

“If Russia is faced with the choice of losing Crimea or using battlefield nukes, they will choose the latter,” he answered

“We’ve already sanctioned/cutoff Russia in every possible way, so what more do they have left to lose?

“If we nuke Russia back, they will nuke us and then we have WW3.”

“Whether one likes it or not, Crimea is absolutely seen as a core part of Russia by Russia,” he added as a follow-up tweet.

“Crimea is also of critical national security importance to Russia, as it is their southern navy base.

“From their standpoint, losing Crimea is like USA losing Hawaii and Pearl Harbor.”

Musk was challenged by some social media users with one claiming his comments were conjecture and only his view on the importance of Crimea to Russia.

The Twitter user Kadubai11 added that NATO and the U.S. made it very clear the Russian army would be destroyed if it chose to go nuclear.

Musk replied: “If Russia faces destruction of their army and utter defeat by NATO, they will use nukes, then NATO will respond with nukes and civilization is over.

“But, hey, look on the bright side! At least Russia doesn’t get Crimea in that scenario, so you can be comforted by that thought, while watching the mushroom clouds rise.”

Musk also made a jab at NATO as he reflected on a new story highlighting NATO has begun its nuclear war games this week. He tweeted: “Practice makes perfect, bolstering up his belief that nuclear war could quickly erupt.

Newsweek has contacted Ukraine’s Ministry of Foreign Affairs for comment.