PARIS — The interim leader that Marine Le Pen chose to run her far-right party while she ran for the presidency has been forced to step down because he praised a Holocaust denier and expressed doubt that the Nazis used poison gas to murder Jews.

Jean-François Jalkh, who had been temporarily at the helm of her National Front, said in a 2000 interview that Zyklon B, the gas used to kill millions of Jews during the Holocaust, would have been “impossible” to use in “mass exterminations.”

Ms. Le Pen called the outrage directed at Mr. Jalkh a “defamation” on Friday morning.

The negative news, however, was somewhat offset by day’s end, when Ms. Le Pen got an endorsement from a defeated right-wing presidential candidate, Nicolas Dupont-Aignan, who won less than 5 percent of the vote nationwide.

“Marine Le Pen is not on the far right to me,” he said.

Ms. Le Pen is one of two candidates to advance to the second round of the presidential race, and announced on Monday that she would temporarily step down as National Front leader to focus on defeating the independent centrist Emmanuel Macron, considered to be the favorite in the election on May 7.