Vladimir Putin has described as “rude” Joe Biden’s comments in which the American president called the Russian leader a “crazy SOB”. Biden was talking about the climate crisis on Wednesday when he said: “We have a crazy SOB like Putin and others, and we always have to worry about nuclear conflict, but the existential threat to humanity is climate.” On Thursday, after a flight onboard a strategic bomber that is capable of carrying nuclear warheads, Putin responded “yes, rude” to a reporter who said Biden had made a rude remark about him. Referring to earlier remarks in which the Russian leader said Biden was a preferable president for Russia than Donald Trump, Putin joked: “It’s not like he can say to me, ‘Volodya, thank you, well done, you’ve helped me a lot’.” He added with a smile: “You asked me which is better for us. I said it then that, and I still think I can repeat it: Biden.” The Kremlin earlier in the day said Biden’s comments were a “disgrace” for the US. “The use of such language against the head of another state by the president of the United States is unlikely to infringe on our president, President Putin,” the Kremlin spokesperson, Dmitry Peskov, said. “But it debases those who use such vocabulary.” The remarks were “probably some kind of attempt to look like a Hollywood cowboy”, Peskov added. The US president has previously called Putin a killer, a pure thug, a war criminal and a butcher. Shortly after Putin’s invasion of Ukraine, Biden said the Russian president “cannot stay in power”. Speaking to donors at a private San Francisco home on Wednesday as part of a three-day trip through California to raise money for his 2024 re-election campaign, Biden also said he was astounded by recent comments made by his likely Republican challenger. Meanwhile, Donald Trump compared Navalny’s suspicious prison death to his own legal troubles in the US. Trump was fined $350m after a New York judge found he lied for years about his wealth on financial statements in his companies. He said the ruling was a form of “communism or fascism”. Biden responded: “Some of the things that this fellow’s been saying, like he’s comparing himself to Navalny and saying that – because our country’s become a communist country, he was persecuted, just like Navalny was persecuted. I don’t know where the hell this comes from. “I mean, if I stood here 10, 15 years ago and said any of this, you’d all think I should be committed,” he said. “It astounds me.” Biden has a tendency to go off script during election fundraisers and in recent months has made apparently unplanned remarks about the Chinese president, the Republican party and Israel, a US ally, for its bombing of the Gaza Strip. Biden’s verbal attacks against Putin have sharply intensified at the White House and on the campaign trail. Last week, the US president blamed Putin and “his thugs” for Navalny’s death. “We don’t know exactly what happened, but there is no doubt that the death of Nalvany was a consequence of something that Putin and his thugs did,” Biden said at the White House. The Kremlin has denied involvement in Navalny’s death and said western claims that Putin was responsible were unacceptable. Putin’s comments on Thursday came after he flew on one of Russia’s newest strategic bombers, which is capable of carrying nuclear warheads, in a thinly veiled reminder to the west of Moscow’s nuclear capabilities. State TV footage showed him sitting alongside a pilot mid-air followed by a scene showing the president clambering down a ladder from the jet. “This is really a new machine, new in many ways. The control is easier. You can see even with the naked, untrained eye,” Putin told a group of state reporters after disembarking. After the jet flight, Putin got into a Kamaz truck for a meeting with the heads of the domestic vehicle industry. For years, the Russian president has cultivated a macho image at home, with antics such as fishing while stripped to the waist, and riding a motorcycle with leather-clad bikers.