U.S. President Donald Trump lashed out at London Mayor Sadiq Khan on Sunday, after the mayor urged city residents to remain calm following a deadly terrorist attack in the British capital.

"At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'" Trump tweeted, several hours after promoting his controversial travel ban as an extra level of security for Americans in light of the attack.

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Trump was apparently responding to comments made by Khan in an interview earlier in the day, in which he said: "Londoners will see an increased police presence today and over the course of the next few days - no reason to be alarmed."

>> London terror attack: Here's everything we know so far | After terror attack in London, Trump says U.S. must be 'smart, needs travel ban' >>

In the attack late on Saturday, three assailants drove a van at pedestrians on London Bridge before getting out of the van in the bustling Borough Market area and stabbing a number of people. All three attackers were shot dead by police within eight minutes of the first emergency call to officers.

In a subsequent tweet, Trump said: "Do you notice we are not having a gun debate right now? That's because they used knives and a truck!"

Khan has been an outspoken critic of Trump and has called on the British government to withdraw its invitation to the U.S. president in light of his executive order barring entry to the U.S. for visitors from several Muslim countries.

In March, Trump's eldest son Donald Trump Jr. raised the furor of many Brits after tweeting insults at Khan in the midst of a terror attack on Parliament.

“You have to be kidding me?!” the young Trump — like his father an avid fan of social media — tweeted out, as details of the attack became clear. “Terror attacks are part of living in big city, says London Mayor Sadiq Khan.”

The seemingly out-of-nowhere swipe turns out to be connected to an article from last September in the British newspaper The Independent. In an interview, Khan was quoted reacting to a bombing in the Chelsea neighborhood of New York City, saying that terrorism preparedness, including providing sufficient support to the police, was “part and parcel of living in a great global city.”

Trump’s mischaracterization of the popular London mayor’s remarks and the questionable timing of his twitter musings did not sit well with many Brits. “You dug this up specifically to garner twitter traffic when people are dying/ injured. How does this help? SAD [(c)Your Dad],” tweeted one.