“Another attack in London by a loser terrorist,” the President tweeted, hours after an improvised explosive device detonated in the London subway system.
He added: “The travel ban into the United States should be far larger, tougher and more specific – but stupidly, that would not be politically correct!”
Later, in an appearance at the White House Rose Garden, Mr Trump said the country must be “smarter” when it comes to terrorism.
“It’s a terrible thing,” he said of the London attack. “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.”
The US Supreme Court allowed a partial version of Mr Trump’s ban to be implemented in June. The ban has been plagued with legal challenges since its inception, with many claiming it amounts to an unconstitutional ban on Muslims.