The Kremlin has accused Joe Biden of attempting to appear like a “Hollywood cowboy” after the US president called Vladimir Putin “a crazy SOB”.
Mr Biden made the comments at a public fundraising event on Wednesday in California, warning about the threat of nuclear conflict.
In response, Kremlin spokesman Dmitry Peskov called it a poor attempt to appear like a “Hollywood cowboy”.
He added that such vocabulary “debases America itself”.
In a brief speech in San Francisco, Mr Biden said: “We have a crazy SOB like that guy Putin, and others, and we always have to worry about nuclear conflict, but the existential threat to humanity is climate.”
It is not the first time the US president has used the offensive term. In a hot-mic slip in 2022, Mr Biden called a Fox News journalist a “son of a bitch”.
He has also called Mr Putin a “butcher” and a “war criminal” in the past.
The Kremlin spokesman said it was “unlikely to infringe on our president, President Putin. But it debases those who use such vocabulary”.
Mr Peskov said the remark was “probably some kind of attempt to look like a Hollywood cowboy. But honestly I don’t think it’s possible”.
“Has Mr Putin ever used one crude word to address you? This has never happened. Therefore, I think that such vocabulary debases America itself,” he added.
In California, Mr Biden also took aim at Donald Trump, who he is likely to face off against in November’s presidential election.
Mr Trump has appeared to compare himself to Alexei Navalny, the Russian opposition activist who died in jail last week.
The Republican has not assigned blame to Mr Putin for Navalny’s death, while Mr Biden said there can be “no doubt” the Russian president was responsible.
“If I stood here 10 to 15 years ago and said all this, you’d all think I should be committed,” Mr Biden said.
Last week, Mr Putin raised some eyebrows when he said he would rather Mr Biden take the presidency over Mr Trump in November.
“He’s more experienced, he’s predictable, he’s an old-style politician,” Mr Putin told Russian TV.