Story highlights London mayor says he has more important things to do than respond to tweet

Khan and Trump had sharp words for each other during the campaign

(CNN) A day after a terror attack in his city left three people dead and as many as 40 wounded, London Mayor Sadiq Khan says he has more important things to do than respond to a tweet from Donald Trump Jr.

Wednesday, President Trump's son tweeted, "You have to be kidding me?!" in response Khan's assertion in 2016 to The Independent newspaper that terror attacks are "part and parcel" of living in a major city.

"I'm not going to respond to a tweet from Donald Trump Jr.," Khan told CNN's Christiane Amanpour on Thursday. "I've been doing far more important things over the last 24 hours."

Donald Trump Jr. manages the Trump Organization and has no role in the White House, but he remains an occasional surrogate for his father. 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.

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

"You have to be kidding me?!" Trump Jr. tweeted, as he shared a September 2016 article from The Independent, and paraphrased its headline as: "Terror attacks are part of living in big city, says London Mayor Sadiq Khan"

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