President Donald Trump repeatedly addressed the possibility of a U.S. nuclear attack on North Korea in a private call last month with Philippine President Rodrigo Duterte, according to a transcript of the call obtained by The Intercept.

“We can’t let a madman with nuclear weapons let on the loose like that. We have a lot of firepower, more than he has times 20, but we don’t want to use it,” Trump told Duterte. (In fact, the U.S. has 6,800 nuclear warheads and North Korea is thought to have about 10.) “You will be in good shape,” he added.

“We have a lot of firepower over there. We have two submarines — the best in the world — we have two nuclear submarines — not that we want to use them at all,” Trump said. “I’ve never seen anything like they are, but we don’t have to use this, but he could be crazy so we will see what happens.”

The call took place on April 29. The transcript, an official Philippine Department of Foreign Affairs document, contains numerous typographical errors. Multiple government sources contacted by the Philippine news outlet Rappler, which collaborated with The Intercept on this story, confirmed its authenticity.

During the call, Trump echoed his publicly stated position that he wants China to take the lead in addressing potential threats from North Korea. “I hope China solves the problem. They really have the means because a great degree of their stuff come [sic] through China,” Trump said. “But if China doesn’t do it, we will do it.”

Duterte then volunteered to call Chinese President Xi Jinping, adding, “The other option is a nuclear blast which is not good for everybody.” Both leaders expressed a preference for avoiding a nuclear confrontation, but nonetheless, Joe Cirincione, president of the Ploughshares Fund and a leading expert on nuclear weapons, was alarmed by the exchange.

“Trump has a disturbing tendency to talk very cavalierly about nuclear weapons — as if he is an impulse away from using them,” Cirincione said. “He doesn’t seem to understand the vast destructive nature of these weapons and the line he would be crossing by using them.”

During the Obama administration, Duterte made clear his disdain for the U.S. president, who he repeatedly called the “son of a whore.” The Obama administration’s measured criticism of Duterte’s murderous war on drugs enraged the Philippine leader. At one point, Duterte threatened to “say goodbye” to a U.S.-oriented foreign policy in favor of a closer alliance with China. Beijing has offered to train Philippine anti-drug forces tasked with carrying out what human rights advocates characterize as an extrajudicial killing campaign.

Duterte welcomed Trump’s election victory. Recently, he has publicly counseled restraint and the de-escalation of tensions with North Korea, even to the point of criticizing the U.S. for its bellicosity. “There seems to be two countries playing with their toys and those toys are not really to entertain,” he said at an April news conference in Manila.