Tensions between Italy and France have deepened after the Italian deputy prime minister urged French people not to support Emmanuel Macron in forthcoming elections, provoking a withering response from Paris.

Matteo Salvini called on voters to shun the French president’s En Marche party in European parliamentary elections in May, prompting Nathalie Loisseau, France’s European affairs minister, to dismiss his comments as insignificant and insisting they would not trigger a “competition of the stupidest”.

“In France they have a bad government and a bad president of the Republic,” Salvini, who also leads the far-right Northern League, wrote on Facebook. “Macron speaks about being welcoming, but then rejects immigrants at the border. The French people deserve better and the European elections of 26 May will provide a good signal.”

To stoke the fire further, Luca Morisi, Salvini’s social media strategist, posted a photo of the minister with Marine Le Pen, his French far-right counterpart who was defeated by Macron in the 2017 elections, on his Facebook page alongside the caption: “Matteo + Marine, Macron’s worst nightmare!” Salvini has forged a partnership with Le Pen as part of a nationalist drive to “save the real Europe” in the EU elections.

Salvini seized the opportunity to attack Macron after Luigi Di Maio, his coalition partner and leader of the anti-establishment Five Star Movement, caused a storm by accusing France of creating poverty in Africa and causing mass migration to Europe. The Italian envoy in France, Teresa Castaldo, was summoned on Monday over what the French foreign ministry described as “hostile” remarks.

In response, Loisseau said the insults were “useless” and would have no effect on French policy. She said: “In France, we have an expression that says whatever is excessive is insignificant. When remarks are excessive … they are, therefore, insignificant.” She added she would not be visiting Italy until “the climate calms.”

Salvini also called on Macron to return 14 Italian fugitives living in France. It is the second time he has made the request since Cesare Battisti, a former leftwing guerrilla fighter convicted of four murders in the late 1970s, was extradited from South America last week after almost 40 years on the run. “I would like the French president to show the same good sense as [Brazilian president Jair] Bolsonaro did,” Salvini said.

Italy and France enjoyed good relations before the coalition came to power last June. Things got off to a bad start after Macron spoke about “populist leprosy” in a reported dig against the new government.