President Donald Trump's suggestion London police could have done more to prevent Friday's homemade bomb explosion has drawn a quick rejoinder from Theresa May.
The British prime minister has told journalists it's never "helpful for anybody to speculate on what is an ongoing investigation".
Trump turned the London subway bomb explosion into an opportunity to highlight his tough talk on terror.
His series of early-morning tweets about the still-unfolding investigation stood in contrast to his delay last month in firmly condemning Neo-Nazis and white supremacists after racial violence broke out in Charlottesville, Virginia, and left one person dead.
At that time, he said: "When I make a statement, I like to be correct. I want the facts. ... I don't want to rush into a statement."
The London bomb exploded on a packed train during morning rush hour Friday, leaving at least 29 people injured but no one with life-threatening injuries.
Police say the explosion is a terrorist attack, the fifth in Britain this year.
On Twitter, 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."
Trump told reporters Friday morning he had been briefed on the explosion but did not provide further details.
National Security Adviser H.R. McMaster suggested later Trump was speaking generally.
Noting that law enforcement has been working to combat terrorism for years, McMaster said: "If there was a terrorist attack here, God forbid, that we would say that they were in the sights of the FBI.
"I think he means generally that this kind of activity is what we are trying to prevent," McMaster said.
The White House said Trump and May spoke Friday.
White House spokeswoman Sarah Huckabee Sanders said Trump's tweet "may have come up" but gave no further detail.
At an event at Joint Base Andrews in Maryland, Trump said he offered prayers for London and said "radical Islamic terrorism it will be eradicated, believe me".