The US State Department has issued a travel warning for citizens travelling to Europe following a string of deadly attacks in Brussels, Belgium.
The travel alert, which was issued on Tuesday and expires on June 20, advises US citizens to be vigilant when in public places or using public transportation.
“Terrorist groups continue to plan near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurants, and transportation,” it said in a statement.
US airlines, meanwhile, canceled travel to and from Brussels on Tuesday after two explosions blew out the Belgian capital’s international airport and a third blast rocked a metro station, leaving at least 30 people dead.
Some of the busiest airports in the US were placed on high security status with a heavy law enforcement presence.
The State Department said a number of US citizens had been injured in Brussels, including three Mormon missionaries and an Air Force member and his family.


US President Barack Obama condemned the terrorist attacks in a brief speech in Havana on his historic visit to Cuba.
“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,” Obama said.
“We can and we will defeat those who threaten the safety and security of people all around the world,” he added.
The bombings also reverberated through the US presidential campaign.
The Republican candidates intensified their criticism of Obama’s handling of the war on Daesh (ISIL), proposing a number of extreme measures to protect the US homeland.
GOP frontrunner Donald Trump, who created a stir last year by proposing a total “shutdown” on Muslims entering the US, renewed his call to “close up our borders.”
“If they could expand the laws, I would do a lot more than waterboarding. You have to get the information from these people,” the billionaire businessman said on NBC’s “Today” program.

His rival, Senator Ted Cruz of Texas, said US authorities should “immediately halt the flow of refugees from countries with a significant al-Qaeda or ISIS presence.”
Despite the harsh rhetoric, US Homeland Security Secretary Jeh Johnson said the agency had no intelligence that a similar attack was being plotted against the US.