Cécile Kyenge, the first black politician to serve in Italy's government, is being sued for defamation by the leader of the country's far-right League party.

Matteo Salvini, Italy’s interior minister and the leader of the hardline anti-immigration League, launched the lawsuit against Ms Kyenge four years after she called his party racist.

A string of politicians from the League party have attacked Ms Kyenge, an eye doctor who was born in Congo but lived in Italy since she was a 19-year-old student, in starkly racist terms over the years.

Now 38 ethnic minority politicians, including dozens of Labour MPs, have signed an open letter in solidarity with Ms Kyenge.

While the Democratic Party member was minister for integration from 2013 to 2014 – becoming the first black minister in Italian history – she was regularly the target of racial slurs from the League party.

One League senator, Roberto Caldaroli, compared her to an orangutan, while an MEP said Ms Kyenge wanted to impose her “tribal traditions” on Italy and was running a “bonga bonga government”.

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A councillor even wrote on Facebook in 2013 that Ms Kyenge should be raped so she would “know what it feels like” when an Italian woman was allegedly attacked by an African migrant.

Last month Mr Salvini began legal proceedings against Ms Kyenge over comments made in an interview in 2014, at the height of the racist furore. Responding to a picture posted by a League politician depicting her as an orangutan, she said the party was racist.

At the time, the League was a fringe, separatist party which sought independence for Northern Italy, but it has since surged in popularity.

In March’s general election the League entered government for the first time, in coalition with the populist Five Star Movement, with its leader Mr Salvini claiming the post of interior minister.

Ms Kyenge, who is no longer an MP and instead now sits in the European Parliament, was defiant after the lawsuit emerged.

On Facebook she wrote: “Salvini has summoned me to court because I said the League is racist. Judge for yourself,” and then posted a series of headlines of League politicians making racist remarks.

On Friday, 38 politicians from across Europe, including 22 Labour MPs, added their names to an open letter condemning the regional court in Piacenza for allowing Mr Salvini’s defamation case to proceed.

“The image on social media is one of many incidents and intimidations by the League’s politicians and supporters that Cécile has recently faced. We fully support Cécile and stand with her decision to remove her parliamentary immunity to fight against racism, xenophobia and other forms of intolerance,” the letter said.

“We also want to state our concern that Cécile’s case represents a wider problem across Europe where we are witnessing the rise of populist, far-right parties in government who are pushing their nationalist agenda and spreading fear and hate against minorities.

“Only last week, the Italian League president and minister of home affairs, Matteo Salvini, compared African migrants to slaves.”