Turkish President Abdullah Gul, who is paying a four-day visit to Germany, cancelled a speech Monday at Berlin's Humboldt University after an anonymous telephoned bomb threat to police, DPA reported.
Police asked the audience to leave the lecture hall and cordoned off the capital's main Unter den Linden street outside the building.
Several hundred Kurds had gathered outside to demonstrate for the release of Abdullah Ocalan, the leader of the Kurdish Workers' Party.
City police said the caller was difficult to understand but seemed to be threatening, and police had assessed the danger as significant.
Gul had been scheduled to speak on the history of relations between Germany and Turkey. He had been welcomed to Berlin earlier Monday, the second day of his stay, and remains in Germany until Wednesday.