President Donald Trump's suggestion that London police could have done more to prevent a homemade bomb explosion drew speedy pushback from British Prime Minister Theresa May.
In a series of early-morning tweets, Trump called the explosion another attack "by a loser terrorist."
He also offered implied criticism of law enforcement, saying "these are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"
Asked about Trump's comments, May said: "I never think it's helpful for anybody to speculate on what is an ongoing investigation."
The bomb exploded on a packed train during morning rush hour Friday (local time), leaving at least 29 people injured but no one with life-threatening injuries. Police said the explosion was a terrorist attack, the fifth in Britain this year.
Trump told reporters Friday morning (local time) that he had been briefed on the explosion, but did not provide further details.
The White House said Trump and May spoke Friday (local time). During the call, Trump offered sympathies and "pledged to continue close collaboration with the United Kingdom to stop attacks worldwide targeting innocent civilians and to combat extremism." The brief statement did not say if the two discussed Trump's tweet.
Trump has lobbed trans-Atlantic criticism after previous attacks.
In June, after attacks in the London Bridge area that claimed seven lives, London Mayor Sadiq Khan warned locals not to be alarmed by the large presence of armed officers on the capital's streets. Trump accused the mayor — whom he has long sparred with — on Twitter of suggesting there was "no reason to be alarmed" by the attack itself.
The president also has had dust-ups with allies over use of intelligence.
In May, British Prime Minister Theresa May protested to Trump after US officials leaked information about a deadly bombing in Manchester.
Photos showing crime scene evidence appeared in US media; the bombing suspect's name was revealed while British officials were still withholding it.
Trump said May was "very angry" over the leaks.
Around that time, the president himself came under fire for reportedly disclosing classified material gathered by close ally Israel. Trump shared the information with Russian officials in an Oval Office meeting.
Trump's rapid reaction Friday contrasts with a statement he made defending his muted response to the violence in Charlottesville last month, when he said he wanted to ensure he had the facts and not make a "quick statement."
Trump also used the moment to argue on Twitter that his travel ban targeting six mostly Muslim nations should be "far larger, tougher and more specific - but stupidly, that would not be politically correct!"
On Twitter, Trump promoted his handling of extremist militants and said the government should cut off the internet to such groups.
"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!," said Trump.
And he argued that his administration has "made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years."
Trump concluded: "Must be proactive & nasty!"