Italian prime minister Matteo Renzi has attacked British Labour party leader Jeremy Corbyn, saying that his recent election proved that Labour “delight in losing”.

“After what happened with Corbyn, I think [David] Cameron is the happiest of all about Corbyn’s win,” said Renzi said in a speech to lawmakers in his own party.

He added: “It’s not a question of being Blairite or anti-Blairite, it’s a matter of ‘Do you want to go to elections like you go to the Olympics, to win or to participate’?”

It was not the first time that Renzi expressed a sense of exasperated frustration in the wake of the Corbyn victory.

Last week, Renzi said on a radio programme: “The last one called ‘Red’ was Ed Miliband, who took a mighty slap in the face from Cameron. I don’t think people who want to get out of Nato want to win elections.”

It is almost unheard of for Renzi to target a foreign opposition leader with such insults, particularly one that, like his Democratic party (PD), is left-of-centre. But Corbyn’s win came at an important juncture for the Italian premier, who is seeking to pass controversial constitutional reforms that are opposed by some in the leftwing flank of the PD.

While some liberals in Italy might take comfort in the Corbyn victory, Renzi – who has taken on trade unions and sometimes forged alliances with conservatives to pass his agenda – was clearly suggesting that they ought not to, and that Corbyn’s chances for moving beyond the opposition were doomed.

He even compared Labour to the Washington Generals, the team that plays in exhibitions against the Harlem Globetrotters basketball team, and always loses.

Blatant attacks against foreign leaders are rare, but Italian politicians do gravitate to British politics. Matteo Salvini, the rightwing and xenophobic leader of the Northern League, voiced his support for David Cameron last month after the prime minister and other conservatives took a hardline against accepting immigrants.

Cameron, Salvini said, had shown “balls” in his efforts to close Britain off to immigrants as thousands sought to make their way to Britain from Calais. While Britain’s stance on immigrants has since evolved, Cameron and Russian president Vladimir Putin are both admired by Salvini.

Beppe Grillo, the populist head of the anti-euro Five Star Movement, has claimed support for Nigel Farage, the Ukip leader, who Grillo once commended for his sense of humour and irony.