Trump's tweets took an apparent dig at British police, implying that they could have done more to stop the attack, which left at least 29 people injured. "We have made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years.Must be proactive & nasty!" the third and fourth tweet of Trump said.
An Islamic State group claimed responsibility for the latest attack to rock Britain - the fifth this year - after a homemade bomb exploded in a packed London subway vehicle Friday, sending panicked passengers fleeing for cover during the morning rush hour.
Meanwhile, the United States president on Friday claimed his administration had "made more progress in the last nine months" against the Daesh (ISIL) terrorist group than his predecessor, Barack Obama.
On Twitter, Trump called the explosion another attack "by a loser terrorist".
Trump was tweeting after a homemade bomb exploded on a packed London subway train during rush hour on Friday. He and his son Donald Trump Jr both mocked Sadiq Khan after taking the mayor's words of reassurance to Londoners out of context.
Lewis Herrington, a terrorism expert at Loughborough University, said that would set it apart from suicide attacks like those on the London subway in 2005 or at Manchester Arena in May, in which the attackers "all wanted to die".
Trump said that the attack was carried out by "a loser terrorist" and urged the U.S.to be proactive in combating terrorism.
"The threat of terrorism that we face is severe, but by working together we will defeat them".
Prime Minister Theresa May summoned a meeting of her government's emergency COBRA committee and described the attack as "cowardly".
The investigation is being led by the Metropolitan Police's counter-terrorism command and involves hundreds of detectives, with support from the intelligence community.
Local residents and businesses rallied together with businesses offering tea and the use of their toilets to people unable to get home.
May responded to the tweet, telling the BBC, "I never think it's helpful for anybody to speculate on what is an ongoing investigation".
And we have to be very smart and we have to be very, very tough, which perhaps we're not almost tough enough.
When asked what he meant about the Muslim ban has to be more specific, Trump said, "we have to be smarter". "People may see that on their travels", said Cuomo.
Trump has repeatedly pointed to his travel ban as a cornerstone of his counterterrorism platform.