The PKK supporters staged a rally to protest the conditions of imprisonment of the terror group's jailed leader Abdullah Öcalan, which then turned violent.
The terrorist sympathizers hurled rocks and projectiles, breaking the Agora building's windows and glass doors, and set trash bins on fire. Police were also targeted by the demonstrators.
Forty-three PKK supporters were detained over the attack on the Council of Europe building.
Director of Communications at the Council of Europe Daniel Holtgen said the terror supporters' "violence and vandalism are unacceptable."
Intensive security measures have been taken in the area the demonstration took place in.