Trump’s assessment followed news of an explosion in a London subway car during the morning rush hour that injured at least 18 commuters and was labeled a terrorist attack by police.
“Another attack in London by a loser terrorist,” Trump said in early morning tweets.
“These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!” Trump added, referring to the police force in London.
It was unclear whether Trump had been briefed by his security advisers, and what information, if any, they provided about the identity of the assailants. Neither the Metropolitan Police nor the British government have said anything publicly beyond describing the detonation as a suspected terrorist attack.
In a subsequent tweet, Trump said: “Loser terrorists must be dealt with in a much tougher manner. The internet is their main recruitment tool which we must cut off & use better!”
The White House did not immediately respond to a question about what information Trump used to craft his tweets.
Asked about Trump’s tweets during a television interview, British Prime Minister Theresa May said: “I never think it’s helpful for anyone to speculate on what is an ongoing investigation.”
May’s former chief of staff, Nick Timothy, was more blunt in his criticism of Trump, writing on Twitter: “True or not — and I'm sure he doesn't know — this is so unhelpful from leader of our ally and intelligence partner.”
During a brief appearance in the Rose Garden on Friday, Trump called the attacks “a terrible thing.”
“It keeps going and going, and we have to be very smart, and we have to be very, very tough — perhaps we’re not nearly tough enough,” he said.
Trump said he had been briefed on the attack and told reporters he plans to call May.
Trump's travel ban blocked the entry of citizens from six Muslim-majority countries for 90 days and all refugees for 120 days. Officials have said the 90-day period will expire in less than two weeks, and Trump will face a critical decision about the ban's future.
The Department of Homeland Security has been working on a report about countries that U.S. authorities say do not provide adequate information to vet their travelers. That report could inform a more expansive measure that bars people from coming to the United States.
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 because of their nationality. The Homeland Security report is expected to be presented to the White House in the coming weeks.
The Supreme Court is scheduled to hear arguments on whether the travel ban is legal on Oct. 10. But by that time, a critical portion of the directive will have expired, and a new measure might be in place. A person familiar with the ongoing discussions said a new ban might make the Supreme Court case moot, but could spark new legal challenges. A permanent ban, in particular, might be harder to defend in court, the person said. It is also possible, though unlikely, that Trump could merely let the ban expire.
In a later tweet on Friday morning, Trump took credit for progress by his administration in combating the Islamic State terrorist group, asserting that more had been done in the past nine months than under Obama’s eight years in office.
“Must be proactive & nasty!” Trump wrote.