German Defence Minister Karl-Theodor zu Guttenberg has stepped down after he was found to have copied large parts of his university doctorate. Mr Guttenberg, considered until recently a possible candidate for chancellor, has already been stripped of his PhD. He told a news conference that it was "the most painful step of my life". More than 20,000 German academics wrote to Chancellor Angela Merkel on Monday complaining he was still in his job. But Ms Merkel had continued to stand by him, with her party facing three state elections later this month. Mr Guttenberg told reporters in Berlin that he was relinquishing all his political offices and he thanked the chancellor for her support, trust and understanding. "I must agree with my enemies who say that I was not appointed minister for self-defence, but defence minister," he said. "I was always ready to fight, but have to admit I have reached the limit of my strength." A 39-year-old aristocrat popular with the electorate, Karl-Theodor zu Guttenberg is a member of the Christian Social Union (CSU), the Bavarian sister party of the chancellor's Christian Democrats. He came under pressure after a Bremen University law professor began reviewing his 2006 thesis with the aid of the internet. Reports emerged of a passage from a newspaper article that featured word for word, and then of a paragraph from the US embassy website being used without attribution. Analysts then estimated that more than half of the 475-page thesis had long sections lifted from other people's work. Eventually the University of Bayreuth that had awarded him a doctorate decided that Mr Guttenberg had "violated scientific duties to a considerable extent". He had already prompted opposition criticism in December for taking his TV presenter wife on a visit to German troops in Afghanistan complete with a large corps of press photographers. The plagiarism scandal led to him being nicknamed Baron Cut-and-Paste, Zu Copyberg and Zu Googleberg by the German media. Source: BBC