Global leaders have called for concerted international cooperation to minimize the risk of further attacks after the strikes early on Tuesday in Brussels claimed by "Islamic State."

"This is another low by the terrorists in the service of hatred and violence," European Commission president Donald Tusk said Tuesday.

"Our disgust is just as boundless as our determination to fight terrorism," Merkel said in a speech at the chancellery. She added that Europe "will emerge stronger" from the challenge.

Merkel said her cabinet would hold an extraordinary meeting on Wednesday to discuss the consequences of the attacks.

German Foreign Minister Frank-Walter Steinmeier, meanwhile, said: "Europe stands together and as one. Belgium is not alone."

In France, President Francois Hollande said: "The whole of Europe has been hit," urging the continent to take "vital steps in the face of the seriousness of the threat…This attack targets Belgium, but Europe as a whole is hit.”

US 'will do what is necessary'

US President Barack Obama said the US would do "whatever is necessary to support our friend and ally Belgium," in the wake of terrorist attacks. "We must unite, we must be together regardless of nationality or race or faith in standing against the scourge of terrorism," Obama said during his visit to Cuba.

US State Department spokesman John Kirby said: "The United States stands with the people of Belgium. We are ready to support the investigation as appropriate." The White House said the U.S. was in contact with Belgian officials about the explosions at the Brussels airport and subway system.

Republican frontrunner Donald Trump said the cause of the bloodshed was "no assimilation" by immigrants. "Belgium is not the Belgium you and I knew from 20 years ago, which was one of the most beautiful and safest cities in the world," Trump told NBC. "Belgium is a horror show right now. Terrible things are happening. People are leaving. People are afraid. This all happened because, frankly, there's no assimilation."

Putin calls for international coperation

Russian President Vladimir Putin attacked what he called "barbarous crimes" and expressed his condolences with Belgium. "(They) demonstrate once again that terrorism has no borders and threatens people around the world. Fighting this evil calls for the most active international cooperation."

Meanwhile, Russian Prime Minister Dmitry Medvedev has called the head of the Ukrainian security service a "halfwit," after the latter said Moscow might be involved in Tuesday's attacks in Brussels. Gritsak had said he “would not be surprised if it turns out that the Brussels attacks were an element of hybrid war waged by Russia.”

'Attacks could have happened anywhere'

"We will never let these terrorists win," said British Prime Minister David Cameron. "We face a very real terrorist threat right across the different countries of Europe and we have to meet that with everything we have." Cameron said the attacks could just as well have happened in Germany or the UK. “We face a very real terrorist threat right across the different countries of Europe and we have to meet that with everything we have."

Canadian Prime Minister Justin Trudeau said: "My thoughts are with the victims as we stand with Belgium and the EU."

"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," meaning "We are all citizens of Brussels."

Spanish Prime Minister Mariano Rajoy said: "Terrorism will never defeat us. The union of democrats in Europe will always prevail over barbarism and madness."

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 tweeted: "My heart and spirit in Brussels, Europe," while Interior Minister Angelino Alfano said "the Brussels attacks strike the heart of our Europe."

Dutch Prime Minister Mark Rutte said neighboring Belgium had "again been hit by cowardly and murderous attacks. Our hearts go out to the victims and next of kin. The Netherlands stands ready to help and support our southern neighbors in any possible way." Rutte said that "extra alertness is necessary, also in our country. We will take all necessary precautionary measures."

Brussels comes on the heels of Turkish attacks

Turkish Prime Minister Ahmet Davutoglu said the attacks "have once again shown the worldwide character of terrorism." Foreign Minister Volkan Bozkir added: "Every effort must continue to fight terrorism without distinction and those who support terrorism."

Pope implores end to violence

Pope Francis described the attacks as "blind violence, which causes so much suffering."

"Imploring the gift of peace from God, (the pontiff) invokes divine blessings on the bereaved families and the Belgian people," he said in a message to Jozef De Kesel, the archbishop of Mechelen-Brussels.

In Egypt, Sunni Islam's leading seat of learning, Al-Azhar, said the blasts "violate the tolerant teachings of Islam" and urged the international community to confront the "epidemic" of terrorism.

jh/msh (AP, AFP)