Francois Hollande: 'The whole of Europe has been hit'

World leaders and senior figures expressed compassion and concern to the attacks in Brussels that killed at least 26 people and injured dozens more on Tuesday morning, when blasts went off at Brussels Zaventem Airport and on the city's subway.

Months after attacks in Paris by Islamic extremists left 129 dead, French President Francois Hollande called the events an attack on all of Europe.

Anne Hidalgo, the mayor of Paris, said the Eiffel Tower would be lit up in the colors of the Belgian flag.

"I am shocked and concerned by the events in Brussels. We will do everything we can to help," British Prime Minister David Cameron posted on Twitter.

Russian President Vladimir Putin said the blasts "show once more that terrorism knows no borders and threatens people all over the world," the AFP reported, citing a Kremlin statement.

German Chancellor Angela Merkel's chief of staff Peter Altmeier called for solidarity with Belgium, in a tweet. "Terrorists will never win."

Republican Donald Trump was the first U.S. presidential candidate to weigh in on the attacks.

"Do you all remember how beautiful and safe a place Brussels wss (sic)," Trump posted on Twitter. "Not anymore, it is from a different world! U.S. must be vigilant and smart!"

In the wake of the Paris attacks in November, Trump called for increased surveillance on American Muslims and proposed a ban on Muslims entering the country.