"Everything humanly possible will be done to fight the threat of terrorism, which can't be swept under the rug," Merkel said from the Chancellery in Berlin.
"Terrorists are enemies of all the values for which Europe and the European Union stand."
Merkel: "Unsere Kraft liegt in unserer Einigkeit. Freie Gesellschaften werden sich als stärker erweisen als Terror." pic.twitter.com/iBY7PG0cha- tagesschau (@tagesschau) 22. März 2016
The Chancellor added that the German foreign ministry and security services were already working closely with the Belgian government to identify those responsible for the bomb attacks at Brussels airport and against metro passengers on Tuesday morning.
The federal police had earlier issued a statement saying that security at Germany's borders with Belgium, Luxembourg and the Netherlands had been stepped up, as well as at airports and train stations.
Other German leaders and organizations were quick to react on social media to the Brussels attacks.
"Germany mourns together with the Belgian people in these difficult times," Merkel's Social Democratic Party deputy Sigmar Gabriel said.
"Terror won't force Europe to retreat from the values of humanity, openness and freedom."
"The news of the horrific terror attacks on the Brussels airport and the Brussels Metro deeply shocked me," President Joachim Gauck wrote to Belgian King Philip.
"Germany stands at Belgium's side in view of these terrorist acts of violence. Together we will defend our European values, freedom and democracy."
"Shocking news from Brussels. These are simply barbaric acts. Our sympathy goes to the families and friends of the victims," Justice Minister Heiko Maas tweeted.
Schockierende Nachrichten aus #Brüssel. Das sind einfach barbarische Taten. Unsere Mitgefühl gilt den Familien und Freunden der Opfer.- Heiko Maas (@HeikoMaas) 22. März 2016
"Unbelievable. Terrorists can never be allowed to win. Europe's values are stronger than hatred and violence. All solidarity for Brussels and the European Union," Chancellor Angela Merkel's chief of staff Peter Altmaier wrote.
Unfassbar. Die Terroristen dürfen nie gewinnen! Die Werte Europas sind stärker als Hass und Gewalt! Alle Solidarität für Brüssel und die EU.- Peter Altmaier (@peteraltmaier) 22. März 2016
"Just as in the terror attacks in Istanbul and Ankara, the criminals and mass murderers want to spread fear and terror and divide society. Let's not let them do that," Aiman Mazyek, chairman of the Central Council of Muslims in Germany, said in a statement.
"The fury of God and of all mankind will strike [the terrorists]. Their shameful acts will never succeed."