The leader of the French Front National has claimed Nigel Farage slandered her party by calling it "anti-semitic".
Marine Le Pen, 45, told The Sunday Times Mr Farage had made "defamatory" and "extremely disagreeable" statements about her party.
Mr Farage has refused to join Ms Le Pen's right-wing alliance in the European parliament, siding with Nicolas Dupont-Aignan - a member of the EU Democrats party.
He claimed "anti-semitism is still embedded" in the FN and last week referred to the party's "compromising historic baggage", the newspaper reported.
Farage has sided UKIP with the EU Democrats led by Nicolas Dupont-Aignan But Ms Le Pen has hit back, saying: "He is often reproached for the behaviour and comments of... his members.
"Slandering your neighbour to try and make yourself look whiter than white, it's not correct. He's doing it simply for electoral purposes."
Ms Le Pen was joined by UKIP founder Dr Alan Sked, who described Mr Farage as "alcoholic, dim and racist" in an interview with the think-tank Parliament Street.
He said: "He's got no idea. He can repeat things about how nasty the European Union is and how it's a threat to the working class but that's about it.
"Anything sophisticated is beyond his grasp."
It comes after two opinion polls showed UKIP was gaining ground ahead of European Parliament elections in May.
A poll for The Sunday Telegraph puts the party in second place in next month's European Parliament elections, three percentage points behind Labour on 30% and, crucially, pushing the Conservatives into third place.
Another, reported in The Mail On Sunday, reveals Nigel Farage could be on track to win a seat in the House of Commons. According to Survation, UKIP polled 32% in the Hampshire constituency of Eastleigh - four points ahead of the Conservatives - where the party narrowly lost out on winning in a by-election last year.
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