Dozens are feared dead in Belgium's capital after a trio of explosions rocked the city of Brussels. "What we feared has happened, we were hit by blind attacks," Belgian Prime Minister Charles Michel said following two explosions at Zaventem Airport and a third at a Metro station in the suburb of Maalbeek, according to The Associated Press and other outlets. “This is a dark moment for our nation. We need calm and solidarity,” he said. “We know that there are many dead, many injured.” At least one of the explosions is believed to have been caused by a suicide bomber, according to Belgium's top prosecutor. The explosions, just four months after more than 100 people were killed in attacks across Paris, drew swift condemnation from leaders across Europe. "Terrorists struck Brussels but it was Europe that was targeted — and all the world that is concerned," French President Francois Hollande reportedly said. President Barack Obama, speaking in Cuba Tuesday morning, condemned the attacks and said "we will do whatever it takes to support our friends and allies in bringing to justice those who are responsible." “This is yet another reminder that the world must unite, we must be together, regardless of nationality or race or faith, in fighting against the scourge of terrorism,” he said. “We can and will defeat those who threaten the safety and security of people all around the world.” World leaders, presidential candidates, celebrities, media organizations, and more have commented on Twitter to express their shock and condolences. Below are some responses to morning's atrocities in Brussels, and the messages being sent to those who have lost a loved one.