A German police bomb squad Friday destroyed a letter containing an explosive substance that was sent to the Berlin residence of President Joachim Gauck, his office and security sources said.
Gauck, whose post as head of state is largely ceremonial, was not at the Bellevue Palace residence at the time, and no staff were endangered, an office spokeswoman said.
The suspect letter was discovered in routine mail screening and destroyed in a controlled explosion in a remote part of the grounds of the palace in Berlin, said Gauck's office.
Security sources speaking on condition of anonymity confirmed the powder in the envelope was an explosive.
The exact type was not yet known, but there was suspicion it was HMTD, a compound used as an initiating explosive in the mining industry that can be home-made.
The interior ministry said there were no firm clues yet in the case, which was being handled by the federal police.
Gauck, 73, who was a Lutheran Christian pastor in the former communist East Germany and assumed his post as president early last year, is not considered a divisive public figure.