US President Donald Trump's son has criticised London Mayor Sadiq Khan in the immediate aftermath of an attack in the city that killed at least five and wounded about 40 on the grounds of the British Parliament, a media report said.

"You have to be kidding me?!" Donald Trump Jr. tweeted on Wednesday, as he shared an article from The Independent, and paraphrased its headline as: "Terror attacks are part of living in big city, says London Mayor Sadiq Khan."
 

You have to be kidding me?!: Terror attacks are part of living in big city, says London Mayor Sadiq Khan https://t.co/uSm2pwRTjO

— Donald Trump Jr. (@DonaldJTrumpJr) March 22, 2017

Trump's son, Donald Trump Jr., manages the Trump Organisation and has no role in the White House, but he remains an occasional surrogate for his father, CNN reported on Wednesday. 

The younger Trump also occasionally calls out the President's political opponents on Twitter, the venue he chose Wednesday to weigh in on the incident in Britain.

The Independent article, published in September 2016, featured Khan's reaction to a bombing in the Chelsea neighbourhood of New York. 

In it, Khan said that preparedness for terror attacks is "part and parcel of living in a big city," and asked Londoners to be correspondingly "vigilant."

The White House issued a more conciliatory response to the Wednesday terrorist attack. The President spoke by phone with British Prime Minister Theresa May, CNN reported.

While the White House Press Secretary Sean Spicer said it would be "irresponsible" to speculate this soon on what precisely happened or who was responsible.

Khan and Trump Sr. had sharp words for one another during the campaign: Khan, who is Muslim, criticised Trump's immigration ban, and Trump at one point challenged the London Mayor to an I.Q. test.