President Trump began tweeting early Friday morning about thewhen only few details were known.
Mr. Trump blamed the attack on a "loser terrorist."
The explosion at the Parson's Green London Underground train station left at least 22 people injured in a bombing attack, but no one died.
The president then said that the travel ban introduced by his administration should be "far larger, tougher and more specific," though he did not know who might be behind the attack.
British Prime Minister Theresa May, when asked about Mr. Trump's comments on the situation, criticized his remarks.
"I never think it's helpful for anybody to speculate on what is an ongoing investigation," she said, adding that the police and security services are working to discover the full circumstances of the attack and to identify who are responsible.