Obama Condemns 'Outrageous' Brussels Attacks

US President Barack Obama has condemned the "outrageous attacks" in Brussels, which have killed dozens of people and injured more than 200 others, including several Americans.

On the final day of his trip to Cuba, Mr Obama said Tuesday's explosions at Brussels airport and subway system were another reminder the world must unite in "fighting against the scourge of terrorism".

As major US cities ramped up security, he ordered all American flags in the US to be flown at half-staff until Saturday out of respect for the victims.

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The Church of Jesus Christ of Latter-day Saints said three of its missionaries serving in Paris were severely injured in the blasts.

It named the Mormons as Utah natives Richard Norby, 66, Joseph Empey, 20, and 19-year-old Mason Wells.

Mr Wells suffered severe burns and a severed Achilles tendon from one of the blasts, his father told the AP news agency.

Chad Wells said his son was recovering after surgery and was doing OK.

The 19-year-old was near the finish line of the Boston Marathon when two bombs exploded in 2013, a friend told AP. He escaped serious injury.

Mr Empey's parents said their son was grateful and in good spirits after undergoing surgery for shrapnel wounds to both legs. The 20-year-old also suffered second-degree burns to his hands, face and head, Court and Amber Empey said.

An update on Mr Norby's condition was not immediately available.

A US Air Force officer was also injured in Tuesday's attack, along with his wife and four children who were with him at the airport.

Officials identified the officer as a lieutenant colonel stationed at Joint Force Command Brunssum, in the Netherlands. No other details on his condition or that of his family have been released.

The Brussels embassy warned Americans to "take the appropriate steps to bolster your personal security".

Starbucks shut all its coffee shops in Belgium, after the Brussels airport outlet was apparently the location of one of the bombs.

The Department of Homeland Security said there is no "specific, credible intelligence" of a threat to the US.

But it said security would be stepped up at airports across the nation as a precaution.

The main terminal at Denver International Airport was briefly evacuated on Tuesday after authorities were alerted to several suspicious packages.

Officials later gave the all-clear and the terminal was fully reopened to passengers.

Police armed with machine guns patrolled New York's Times Square, while National Guard troops were ordered to John F Kennedy and LaGuardia airports.

Donald Trump, who wants a temporary ban on Muslims entering the US, said America should close its borders "until we figure out what's going on".

The Republican presidential front runner told NBC: "Belgium is a horror show right now.

"People are afraid. This all happened because, frankly, there's no assimilation."

His Republican rival, Ted Cruz, said: "We need to empower law enforcement to patrol and secure Muslim neighborhoods before they become radicalized."

Democratic presidential front runner Hillary Clinton said the attacks would only strengthen US resolve to "defeat terrorism and radical jihadism".