The Greens candidate, who has emerged as the top rival to chancellor candidate Armin Laschet of Angela Merkel’s CDU party, said she used the racial slur while retelling a story about a schoolchild refusing to do an assignment containing the N-word.

“That was wrong and I’m sorry,” Baerbock wrote in a series of tweets on Sunday, saying she was aware of the racist origins of the word and the hurt it causes black people.

The apology is the latest in a series of setbacks for the Green Party’s chancellor candidate as the campaign for the September 26 parliamentary election heats up.

After riding high in voter surveys this spring, support for Baerbock and the Greens fell after she appeared sloppy in declaring party-related income and inflated items on her resume.

More recently, Baerbock has faced claims that a book she wrote on her plans for renewing the nation is rife with plagiarism.

Baerbock said on Twitter that she used the slur during a discussion about anti-Semitism and racism when she had told of an incident at a school in her neighbourhood.

There, a pupil had refused to complete a worksheet on which the racial slur was written.

“Unfortunately, in the recording of the interview, I quoted the word in the emotional description of this unspeakable incident and thus reproduced it myself,” Baerbock wrote.

Baerbock said the offensive word in an interview with the Central Council of Jews in Germany. In the interview, the word has been made inaudible with a beep.