German Education Minister Annette Schavan resigned yesterday after being stripped of her doctorate for alleged plagiarism, in a blow to her ally Angela Merkel.

Four days ago the University of Duesseldorf ruled Schavan, a close confidante of Chancellor Merkel, had "systematically and intentionally" copied parts of her thesis, and withdrew her PhD granted more than 30 years ago.

Merkel lost her defence minister Karl-Theodor zu Guttenberg in a similar scandal two years ago. Schavan said she would fight the university's decision to strip her of her degree.