"The election results must be verified and individuals who have been proven to have participated in violence against peaceful demonstrators must be sanctioned," he wrote on Twitter.
Maas stressed that the European Union intends to "significantly increase the pressure on Belarus."
On August 14, EU foreign ministers will discuss the situation in Belarus at an emergency videoconference.
The head of the European Commission, Ursula von der Leyen, called for sanctions against those who "violate democratic values" in Belarus.