WASHINGTON — President Trump seized on a terrorist attack in London on Friday to promote his ban on travel to the United States by Muslims and, in the process, ran afoul of Britain by claiming without evidence that the assailants had been “in the sights” of the British police.
In a fusillade of early morning tweets, Mr. Trump cited the chaotic scene in a London Underground station as Exhibit A for his hard-line policies. His ban on visitors from predominantly Muslim countries, he wrote, should be “far larger, tougher and more specific” — a statement that seemed calculated to mollify his political base after a week in which Mr. Trump suddenly began playing dealmaker with Democrats on immigration.
But Mr. Trump’s assertion that the assailants had been known to Scotland Yard angered Prime Minister Theresa May, who said it was not helpful for anyone to speculate while an investigation was underway. Mr. Trump was later briefed about the attack and called Mrs. May with condolences, according to a senior official, though he did not apologize.
It was the latest episode in which Mr. Trump was at odds with Britain over sensitive security issues. In June, he criticized London’s mayor, Sadiq Khan, over his response to another terrorist attack, misconstruing Mr. Khan’s words. In March, the White House press secretary at the time, Sean Spicer, repeated allegations that a British intelligence agency had wiretapped Trump Tower, which British authorities dismissed as “utterly ridiculous.”
Trump’s assertions were also a sign that for all the talk about a more disciplined White House under the new chief of staff, John F. Kelly — who has urged the president to have tweets vetted by his aides — Mr. Trump was still determined not to censor himself on social media and was fully capable of roiling the diplomatic waters with a single unguarded post.
At 6:42 a.m., Mr. Trump tweeted that “sick and demented people who were in the sights of Scotland Yard” carried out the attack, which injured at least 29 people in the blast and ensuing panic. It was not clear where Mr. Trump got that information, though 23 minutes earlier, “Fox & Friends,” a program he regularly watches, broadcast a report in which a security analyst said he feared that the London police had already known the identity of the attackers.
“Can someone tell Scotland Yard?” asked Brian Kilmeade, one of the hosts of the program.
White House officials tried to play down the contretemps, saying Mr. Trump was referring to the longstanding efforts of British law enforcement authorities to investigate would-be terrorists, not to anyone involved in Friday’s attack.