World leaders reacted with condemnation and horror Tuesday over the deadly attacks on Brussels airport and a metro station in the Belgian city. 

Prime Minister Justin Trudeau said in a statement he was "outraged and deeply saddened" by news of the attacks.

"Canada stands by Belgium in this difficult time and has offered all possible assistance," said Trudeau. "We will continue to work closely with our allies and the international community to help fight and prevent terrorism here and abroad, and to bring to justice those who are responsible for planning and carrying out these senseless acts."

Global Affairs Canada issued a statement saying, "Our thoughts and deepest sympathies are with those affected by the incidents in Brussels, Belgium." The department said it wasn't immediately aware of any Canadians affected by the attacks.

At a news conference in Ottawa, Global Affairs Minister Sté​phane Dion called it "a black Tuesday for Belgium. Hearing the screams of children in the black smoke of the Belgian metro only strengthens our resolve."

Obama underlines U.S. support

U.S. President Barack Obama, in the midst of a state visit to Cuba, addressed the bombings as he began his first speech in Havana Tuesday morning.

"The thoughts and prayers of the American people are with the people of Belgium," Obama said. "We stand in solidarity with them in condemning these outrageous attacks against innocent people.

"We will do whatever is necessary to support our friend and ally Belgium in bringing to justice those who are responsible. And 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.

"We can and we will defeat those who threaten the safety and security of people all around the world."

Here are other responses from around the world:

France

President François Hollande said, "Terrorists struck Brussels, but it was Europe that was targeted — and all the world that is concerned." Hollande also warned that "this war will be long," so sangfroid and lucidity are needed.

Paris officials announced the city would light the Eiffel Tower in the colours of the Belgian flag. The city's mayor, Anne Hidalgo, described it in a tweet as a measure of "solidarity with Brussels."

Visiting Montreal on Tuesday, the head of France's controversial far-right party Front National issued a warning about the threat of Islamic extremism.

Marine Le Pen told reporters: "I don't get the sense that Islamic fundamentalism is being treated like the threat it really is. And just like I saw in France in the past, here in Canada, whoever condemns Islamic fundamentalism is accused of Islamophobia."

United Kingdom

Prime Minister David Cameron said Britain would do everything it could to help Belgium after the attack. The U.K.'s official terrorist threat level stood at "severe," the second-highest level on a five-point scale, meaning an attack is highly likely.

"This is the latest terrorist outrage, and today is a day for sympathy and condolence, for enhancing our own security, for working with our own colleagues and offering them every help we can and making sure we are very clear that we will never let these terrorists win," Cameron said.

Germany

German Justice Minister Heiko Maas said: "Today is a black day for Europe." He said on Twitter that "the horrible events in Brussels affect us all," adding that "we are steadfastly at the Belgians' side."

Chancellor Angela Merkel has pledged Belgium's prime minister Germany's "full solidarity" following the Brussels attacks and says her cabinet will discuss the bombings on Wednesday.

Merkel spoke with Belgian Prime Minister Charles Michel and promised, "We will work in every way with his government and the Belgian security forces to find those responsible for today's crimes, detain and punish them."

Merkel said, "Our strength lies in our unity, and our free societies will prove to be stronger than terrorism."

Russia

The Kremlin offered its condolences to Belgium and expressed solidarity after the attacks Tuesday.

Russian President Vladimir Putin said the attacks have underlined the need to pool global efforts for combating terrorism.

Putin spoke in televised remarks Tuesday as he met with visiting Finnish President Sauli Niinisto.

Putin began by offering condolences to the families of the victims in Brussels. He added, "We have repeatedly discussed the issues related to the fight against terrorism, and it's possible to efficiently combat it only by united efforts."

Some other Russian officials and lawmakers have criticized Western reluctance to co-operate with Moscow on fighting terrorism amid the strain in Russia-West ties over the Ukrainian crisis.

Russian foreign ministry spokeswoman Maria Zakharova said the West's politics of "double standards" have led to terrorist attacks and that frozen diplomatic relations between NATO and Russia have slowed the fight with terrorism.

Prominent Russian lawmaker Alexei Pushkov also had a jab at Europe and NATO following the Brussels attacks. Pushkov offered his condolences, but said, "It's time for Europe to understand where the genuine threat is coming from and join efforts with Russia."

Austria

The attacks in Belgium "carry a cowardly and barbaric signature," and "Europe must combat terror jointly and determinedly defend its European values," said a joint statement from Austrian Chancellor Werner Faymann and Vice-Chancellor Reinhold Mitterlehner.

United Nations

Members of the UN Security Council said in a statement it "condemned in the strongest terms" the attacks and "expressed their solidarity to Belgium in their fight against terrorism."

The statements also said the council "reaffirmed that terrorism in all its forms and manifestations constitutes one of the most serious threats to international peace and security."

UN spokesman Stephane Dujarric said Secretary General Ban Ki-moon "is confident that Belgium's and Europe's commitment to human rights, democracy and peaceful coexistence will continue to be the true and lasting response to the hatred and violence of which they became a victim today."

Middle East

The Lebanese Shia group Hezbollah said Europe was being burnt by "fire" from Syria and the Middle East which showed the growing threat posed by ultra-radical "takfiri" groups.

"The fire that Europe in particular and the world in general is being burnt by is the same one that some regimes ignited in Syria and other states in the region," Hezbollah said in a statement condemning the attacks.

Syria's government condemned the Brussels attacks, but said they were the "result of wrong policies" on extremism.

Salem Al Meslet, representing a coalition of Syrian opposition groups engaged in peace talks in Geneva, said, "It is with a heavy heart we learned of these ruthless attacks in Brussels.… The world must stand united to defeat terrorism."

U.S. campaign

In the U.S. presidential campaign, events in Brussels drew early comments, mainly from Republican Party presidential contenders:

  • Donald Trump told Fox News: "We have a worldwide situation that is out of control." He renewed his call to "close up our borders" and put a stop to refugees entering the U.S. from the Middle East. "It's going to get worse and worse, because we are foolish, we are foolish.… We can't allow these people, at this point, to come into the U.S." 
  • Ted Cruz issued a statement saying: "Our hearts break for the men and women of Brussels this morning.… Radical Islam is at war with us. For over seven years we have had a president who refuses to acknowledge this reality. And the truth is, we can never hope to defeat this evil so long as we refuse to even name it. That ends on Jan. 20, 2017, when I am sworn in as president. We will name our enemy — radical Islamic terrorism. And we will defeat it."
  • John Kasich issued a statement saying: "We must also redouble our efforts with our allies to identify, root out and destroy the perpetrators of such acts of evil. We must strengthen our alliances as our way of life and the international system that has been built on our common values since the end of the Second World War comes under challenge from these and other actors of evil. My thoughts and prayers are with the victims of the attacks and with the people of Belgium."

On the Democratic Party side, both candidates commented:

  • Hillary Clinton issued a statement saying in part: "These terrorists seek to undermine the democratic values that are the foundation of our alliance and our way of life, but they will never succeed. Today's attacks will only strengthen our resolve to stand together as allies and defeat terrorism and radical jihadism around the world."
  • Bernie Sanders issued this statement: "We offer our deepest condolences to the families who lost loved ones in this barbaric attack and to the people of Brussels who were the target of another cowardly attempt to terrorize innocent civilians….Today's attack is a brutal reminder that the international community must come together to destroy ISIS. This type of barbarism cannot be allowed to continue."

With files from The Associated Press