WASHINGTON -- U.S. President Donald Trump slammed "political correctness" in a tweet early Sunday in the wake of a deadly terror attack in London.

"We must stop being politically correct and get down to business of security for our people," Mr. Trump tweeted.

"If we don't get smart it will only get worse," he added.

We must stop being politically correct and get down to the business of security for our people. If we don't get smart it will only get worse — Donald J. Trump (@realDonaldTrump) June 4, 2017

The assault in London killed seven people, and it began Saturday night when a van veered off the road and barreled into pedestrians on busy London Bridge. Three men fled the van with large knives and attacked people at bars and restaurants in nearby Borough Market, police and witnesses said. The attack unfolded quickly, and police said officers had shot and killed the three attackers within eight minutes.

Get Breaking News Delivered to Your Inbox

As British Prime Minister Theresa May on Sunday called for tougher measures to contain Islamic extremism in Britain, London Mayor Sadiq Khan said he was "reassured we are one of the safest global cities in the world."

In response, Mr. Trump tweeted, saying, "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'"

At least 7 dead and 48 wounded in terror attack and Mayor of London says there is "no reason to be alarmed!" — Donald J. Trump (@realDonaldTrump) June 4, 2017

The president continued, seemingly bringing up an ongoing debate in the U.S. over Second Amendment rights.

"Do you notice we are not having a gun debate right now?" he posted. "That's because they used knives and a truck!"

Do you notice we are not having a gun debate right now? That's because they used knives and a truck! — Donald J. Trump (@realDonaldTrump) June 4, 2017

The attack in London came as Ariana Grande is set to hold a benefit concert for the victims of a suicide bombing last month in Manchester, England, that killed 22 people and injured dozens of others at the artist's concert.

The Islamic State group claimed responsibility for the Manchester bombing, but there has not yet been a claim of responsibility for the London attack, which Prime Minister May linked to Islamic extremism.