British Prime Minister Theresa May Theresa Mary MayAre US-Japan relations on the rocks? Trump insulted UK's May, called Germany's Merkel 'stupid' in calls: report Bolton says Boris Johnson is 'playing Trump like a fiddle' MORE told President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE she was displeased with his suggestion on Friday that the suspects in a London terrorist attack were "in the sights" of London's Metropolitan Police, Bloomberg reported.

In the immediate aftermath of a bombing on a London train Friday, Trump tweeted that the U.K. government "must be proactive" in its search for suspects and said that police had known of the perpetrators.

"Another attack in London by a loser terrorist," Trump wrote on Twitter. "These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"

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At the time, police had not identified any suspects nor had they arrested anyone in connection with the attack. May said in a television interview Friday that speculation was not helpful in an ongoing investigation.

"I never think it's helpful for anybody to speculate on what is an ongoing investigation," she said.

But according to Bloomberg, the British prime minister expressed her displeasure with Trump's remarks directly to the president himself.

A bomb partially exploded on a London train during the morning rush hour on Friday, injuring 30 people and prompting the government to raise the country's terrorism threat level to "critical."

An 18-year-old man was arrested on Saturday in connection with the attack, though police have not identified or charged him. It's unclear what role authorities believe he may have had in the incident.

Similarly, May fumed to Trump after U.S. media published leaked information about a British police investigation into the bombing of the Manchester Arena in May that killed 22 people.