Germany's defense minister says he is dropping his academic title amid an ongoing investigation into allegations that he plagiarized part of his doctoral thesis.

Karl-Theodor zu Guttenberg said Friday the work "no doubt contains mistakes," but he strongly rejected all plagiarism accusations. He said he would refrain from using the title of Dr. until the outcome from a review of his thesis by Bayreuth University.

Reports emerged earlier this week Guttenberg had copied tracts of his 475-page thesis from other sources without credit.

Polls regularly rate the 39-year-old as Germany's most popular politician, but the plagiarism flap has prompted calls for his resignation.

Chancellor Angela Merkel has backed her minister.