Warren Buffett warned that the spread of nuclear weapons is making the world a more dangerous place, saying the prospect of Iran acquiring a bomb would heighten the risk of a catastrophic conflict.

The Berkshire Hathaway chairman said the growing number of nuclear-armed states has fundamentally altered the global risk landscape, amplifying concerns he has voiced for decades about proliferation.

“Now you’ve got… nine countries,” Buffett said on CNBC’s “Squawk Box” Tuesday. “We worried enormously about it when there were two… You were not dealing with unstable people or anything like that. The ship’s turned around.”

Buffett pointed specifically to rising geopolitical tensions involving Iran and North Korea, suggesting that the potential presence of nuclear weapons in those regions raises the stakes considerably.

“Just think of how you’d feel with North Korea having it and Iran wanting to get it,” he said. “The most dangerous thing is, actually, somebody that’s got their hand on the switch, who is dying themselves, or is facing enormous embarrassment… I don’t know the answer for it, but I do know that… it’ll be more difficult if Iran has the bomb than they don’t.”

The 95-year-old investor has long warned that the spread of nuclear capabilities increases the likelihood of a worst-case scenario. Asked what advice he would give a U.S. president confronting the issue of enriched uranium, Buffett struck a fatalistic tone about the long-term trajectory.

“I would say that one way or another… in the next 100 years — maybe it’s 200 years, who knows — something will happen to cause it to be used,” he said. “And we can’t take what’s out there now.”