Ahead of three state elections in late March, German Chancellor Angela Merkel quickly replaced popular Defence Minister Karl-Theodor zu Guttenberg, who resigned in a row over plagiarism.

Interior Minister Thomas de Maiziere has now been moved to defence, with Hans-Peter Friedrich taking up the interior post.

Guttenberg, who was considered until recently a possible candidate for chancellor, quit on Tuesday after he was found to have copied parts of his university doctorate thesis, thus depriving her conservatives of their brightest star.

"It's important to quickly show clarity and our ability to act," Merkel said at a press conference, speaking of the changes that were announced faster than expected.

"It's right, it's good and helpful that this quickly answers the questions that you would otherwise be asking us."

The scandal had become an embarrassment to Chancellor Angela Merkel.