(Reuters) - Tensions between French National Front leader Marine Le Pen and her father Jean-Marie worsened on Thursday as the 86-year-old founder of the far-right party defended having described Nazi gas chambers as a "detail of history".

Since taking over from her father in 2011, Marine Le Pen has tried to rid the anti-immigrant party of its anti-Semitic image and widen its voter appeal as she readies a bid for the French presidency in 2017.

In a television interview, Jean-Marie Le Pen defended a 1996 comment that gas chambers used to kill Jews in the Holocaust were "merely a detail in the history of World War Two", a remark for which he was convicted of inciting racial hatred and fined.

"I deeply disagree with him. I take note of what he said but I believe that those coming over to vote for us understand what is going on ... He is being deliberately provocative," she told the website of Le Figaro daily.

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While other FN officials have been stripped of their party membership for racism, there has been no move to bar Jean-Marie Le Pen from a party of which he still holds the title of honorary president. He is popular with many FN members and will stand as a candidate in December's regional elections.

The FN founder rejected all accusations of anti-Semitism and defended the gas chamber comment as a self-evidence.

"I stand by this because I believe it is the truth," he told BFM TV. What I said is what I think - the gas chambers were a detail of the history of the war. Unless of course we are suggesting the war was a detail of the gas chambers."

Asked about the current state of the FN, he called it a party for patriots including "fervent Petainists", a reference to Philippe Petain, the general who led the French war-time government that cooperated with Nazi Germany's racial policies.