His assertion that the London attackers "were in the sights of Scotland Yard" was either the revelation of shared intelligence or what the Prime Minister called unhelpful speculation.
He added that his travel ban targeting six mostly Muslim nations should be "far larger, tougher and more specific - but stupidly, that would not be politically correct!"
The travel ban has been ensnared in the courts since Trump's first attempt to enact the policy in January.
A police spokesperson told CNN Trump's comment is "pure speculation given we don't know who is involved". The police has identified the explosion as a terrorist attack. And we have to be very smart and we have to be very, very tough, which perhaps were not almost tough enough.
London and Washington have long boasted of their "special relationship", close ties that were strained earlier this year when the United States leaked information on an investigation into a bomber who killed 22 at a Manchester pop concert.More news: Sunshine State facing power outage and heat, 5 dead at South Florida
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- Donald J. Trump (@realDonaldTrump)Do you notice we are not having a gun debate right now?
Trump's keenness to underline a series of terror attacks in Britain, virtually in real time, has led to a repeated outcry across the Atlantic that has helped indefinitely delay his much-vaunted state visit to the country.
Trump responded on Twitter: "At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'".
Trump's tweet seemed to envision such a "larger, tougher" ban, though he also said the measure needed to be "more specific" - which might indicate the White House is not inclined to bar people merely due to their nationality.
"Another attack in London by a loser terrorist", Trump added. Must be proactive & nasty!'
The Supreme Court is scheduled to hear arguments on whether the travel ban is legal on October 10.