Germany's defense minister quit Tuesday amid persistent allegations that he plagiarized parts of his doctoral thesis, depriving Chancellor Angela Merkel's conservative bloc of a man long rated as the country's most popular politician.

Karl-Theodor zu Guttenberg, 39, said he had decided to go "not just because of my faulty doctoral work" but because the persistent focus on it threatened to overshadow duties such as overseeing a major overhaul of the German military and troops' deployment in Afghanistan.

"It is the most painful step of my life," Guttenberg told reporters in a hastily convened appearance at his ministry. "Because my office, the Bundeswehr, academia and the parties that support me faced potential damage, I am drawing the consequences that I have and would have demanded of others."

Bayreuth University revoked Guttenberg's academic title last week, saying the minister had "seriously violated" its standards by failing to credit sufficiently some of his sources.