Brussels - "Today is a black day for #Europe. The horrible events in #Brussels affect us all. We are steadfastly at the Belgians' side," German Justice Minister Heiko Maas said on Twitter.
Belgium's European partners responded with shock and solidarity Tuesday after "terrorist attacks" at Brussels airport and a city metro station near the European Union's institutional heart left at least 21 people dead.
Russia and Turkey - themselves targets of attacks in recent months - condemned the blasts, saying they bore out the need to fight terrorism.
"Today is a black day for #Europe. The horrible events in #Brussels affect us all. We are steadfastly at the Belgians' side," German Justice Minister Heiko Maas said on Twitter.
"Our Union's capital is under attack. We mourn the dead and pledge to conquer terror through democracy," the Greek foreign ministry said in a tweet.
It added in French,"Nous sommes tous Bruxellois," - "We are all citizens of Brussels."
Swedish Prime Minister Stefan Lofven described the blasts as "an attack against democratic Europe. We will never accept that terrorists attack our open societies."
Italian Prime Minister Matteo Renzi said: "My heart and spirit in Brussels, Europe," while Interior Minister Angelino Alfano said "the Brussels attacks strike the heart of our Europe."
Danish counterpart Lars Lokke Rasmussen denounced the blasts as a "despicable attack."
In other reactions:
-- Russian President Vladimir Putin: The "barbarous crimes... demonstrate once again that terrorism has no borders and threatens people around the world. Fighting this evil calls for the most active international cooperation."
-- Turkish Foreign Minister Volkan Bozkir: "Every effort must continue to fight terrorism without distinction and those who support terrorism."
-- Polish President Andrzej Duda: "The fight against terrorism is the duty of every one of us."
-- Serbian Prime Minister Aleksandar Vucic: "The world is shocked by these terrorist attacks, which jeopardise all the values of civilisation that we strongly support."
-- The Syrian opposition, the High Negotiations Committee (HNC), said: "The people of Syria stand with the people of Belgium in solidarity... The world must stand united to defeat terrorism."