"These were hard days that reminded us that terrorism is more than a national threat, that it requires us to overcome our differences and join efforts in the fight against terrorism," Radev said on his Facebook page late on Tuesday.
He expressed condolences to Russia and Germany, the countries whose nationals died in the attacks.
On Monday, Russian Ambassador in Ankara Andrey Karlov was killed by a Turkish off-duty police officer at an art gallery exhibition opening in Ankara. Three other people were also injured in the attack. The Russian Foreign Ministry said it considers the attack a terrorist act.
Just hours after the ambassador's murder in Turkey, a truck rammed into the crowd at the Berlin Christmas market, killing 12 people and injuring 48. Police have confirmed the ramming was intentional and detained the suspect, a Pakistani migrant, but he was later released over lack of evidence linking him to the attack. The incident is being investigated as a terrorist attack.