Pope Leo has said he has never supported nuclear weapons and that those who criticise him need to speak the truth, in response Donald Trump’s latest tirade accusing him of “endangering a lot of Catholics” with his stance on the Iran war.

Speaking to journalists on Tuesday night after leaving the papal retreat in Castel Gandolfo, near Rome, the first US-born pontiff said: “The mission of the church is to preach the gospel, to preach peace.”

Leo, who is to meet the US secretary of state, Marco Rubio, in the Vatican on Thursday in an effort to ease tensions sparked by previous Trump broadsides, made a plea for honesty in political debate.

“If anyone wants to criticise me for proclaiming the gospel, let them do so with the truth: the church has spoken out against all nuclear weapons for years, there is no doubt about that,” the pope said. “I simply hope to be listened to because of the value of God’s word.”

Earlier in the day, Trump told Hugh Hewitt, a prominent conservative radio talkshow host: “The pope would rather talk about the fact that it’s OK for Iran to have a nuclear weapon, and I don’t think that’s very good.

“I think he’s endangering a lot of Catholics and a lot of people. But I guess if it’s up to the pope, he thinks it’s just fine for Iran to have a nuclear weapon.”

In April, the US president lashed out at Leo in response to the pope’s criticisms of the war on Iran, calling Leo “weak on crime” and “terrible on foreign policy” and saying he had only been elected pontiff because Trump himself was in the White House. Trump then shared an AI-generated image of himself depicted as a Christ-like figure before deleting it.

Leo, who marks his first year as pope on Friday, often goes to Castel Gandolfo at the start of the week, leaving on a Tuesday night and on some occasions stopping to chat to journalists. But until Trump’s latest tirade against him, he had not been planning to speak this week.

“We were told yesterday that there would be no papal chat,” said Andrea Vreede, a Vatican correspondent for the Dutch public radio and TV network NOS. “But there was, because he thought it was necessary and it was necessary.”

Vreede added: “Things have become really tense because Trump isn’t talking about the church or Vatican, but Leo; he has made it personal. We’re back to the middle ages when holy Roman emperors and popes did this kind of [thing], used this kind of language.”

The Rubio meeting will be the first known private audience Leo has had with a member of Trump’s cabinet since the secretary of state and the US vice-president, JD Vance, met the pope a day after his papal inauguration mass in May last year.

A “frank” conversation is expected, the US ambassador to the Holy See, Brian Burch, said, although Rubio has play down the rift between Trump administration and the Vatican, saying “obviously we had some stuff that happened” but there was “a lot to talk about with the Vatican”.

On Friday, Rubio will also meet the Italian prime minister, Giorgia Meloni, whom Trump berated in April after she criticised his remarks against Leo. The president lambasted the Meloni government for not supporting the strikes on Iran and threatening to withdraw US troops from Italy as a result.

But Rubio’s meeting with the pope, which the US secretary of state has been seeking for weeks, could have an ulterior motive, said Vreede.

“For Leo, it’s important to have a photo moment with Rubio and then release a short statement saying they are continuing their dialogue and all want world peace,” she said. “Privately, it won’t be a nice talk, it cannot be a nice talk … but Rubio needs to keep the diplomatic channels with the Vatican open as he’s thinking about himself [ahead of the US presidential elections] in 2028.”

Trump’s rivalry with Rubio possibly triggered his latest outburst, Vreede added: “He believes in rivalry, in winning … perhaps he’s trying to interfere with Rubio because Rubio is being a bit too diplomatic.”