Theresa May has issued a rebuke to Donald Trump, after the US President suggested the person responsible for a suspected terror attack on a London Tube train was “in the sights of Scotland Yard”.

In a surprisingly frank response to a question about a tweet from the President about the attack, the Prime Minister said it was not “helpful” for anyone to start speculating about an ongoing investigation.

It came after Mr Trump took to Twitter in his usual style to comment on the explosion at Parsons Green underground station, and appeared to criticise UK security forces and the way the Government has dealt with terrorism.

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Asked directly about the President’s tweet, Ms May said: “I never think it’s helpful for anybody to speculate on what is an ongoing investigation.”

The Prime Minister was speaking after chairing a meeting of the emergency Cobra committee to update ministers and key security officials on the most recent developments in the investigation.

Mr Trump tweeted a matter of hours after the explosion – which left at least 22 people injured – telling his followers: “Another attack in London by a loser terrorist. These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”

He followed it up with the comment: “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!”

Speaking outside the White House later he called the attack a “terrible thing” and said that governments are not being “nearly tough enough” on terrorists.

Ms May’s apparent rebuke to the President contrasts with previous occasions, when she has been criticised for being too close to him and not sufficiently questioning his views, including those Mr Trump expressed in the wake of the Charlottesville unrest.

Shape Created with Sketch. Parsons Green explosion – in pictures Show all 23 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Parsons Green explosion – in pictures 1/23 Parsons Green explosion An explosion on a packed Tube train has injured a number of people in west London AFP/Getty Images 2/23 Parsons Green explosion The blast triggered a stampede as commuters panicked AFP/Getty Images 3/23 Parsons Green explosion Click through for more pictures from the scene REUTERS 4/23 Parsons Green explosioN REUTERS 5/23 Parsons Green explosion A bucket with flames and wires coming out of it was photographed in the carriage after the explosion – apparently the source of the blast AFP 6/23 Parsons Green explosion PA 7/23 Parsons Green explosion REUTERS 8/23 Parsons Green explosion REUTERS 9/23 Parsons Green explosion AFP/Getty Images 10/23 Parsons Green explosion Reuters 11/23 Parsons Green explosion AFP/Getty Images 12/23 Parsons Green explosion AFP/Getty Images 13/23 Parsons Green explosion REUTERS 14/23 Parsons Green explosion REUTERS 15/23 Getty Images 16/23 Getty Images 17/23 Getty Images 18/23 Getty Images 19/23 AFP/Getty Images 20/23 Getty Images 21/23 AFP/Getty Images 22/23 AFP/Getty Images 23/23 AFP/Getty Images 1/23 Parsons Green explosion An explosion on a packed Tube train has injured a number of people in west London AFP/Getty Images 2/23 Parsons Green explosion The blast triggered a stampede as commuters panicked AFP/Getty Images 3/23 Parsons Green explosion Click through for more pictures from the scene REUTERS 4/23 Parsons Green explosioN REUTERS 5/23 Parsons Green explosion A bucket with flames and wires coming out of it was photographed in the carriage after the explosion – apparently the source of the blast AFP 6/23 Parsons Green explosion PA 7/23 Parsons Green explosion REUTERS 8/23 Parsons Green explosion REUTERS 9/23 Parsons Green explosion AFP/Getty Images 10/23 Parsons Green explosion Reuters 11/23 Parsons Green explosion AFP/Getty Images 12/23 Parsons Green explosion AFP/Getty Images 13/23 Parsons Green explosion REUTERS 14/23 Parsons Green explosion REUTERS 15/23 Getty Images 16/23 Getty Images 17/23 Getty Images 18/23 Getty Images 19/23 AFP/Getty Images 20/23 Getty Images 21/23 AFP/Getty Images 22/23 AFP/Getty Images 23/23 AFP/Getty Images

The Prime Minister also condemned the “cowardly” attack, saying it involved a device “clearly intended to cause significant harm”, and indicated that the terror threat level would remain at severe, meaning an attack is highly likely.

She added: “The police and the security services are obviously doing all the work to discover the full circumstances of this cowardly attack.”

Scotland Yard has declared a terrorist incident after a blast sent a “fireball” and a “wall of flame” through a packed London Underground train this morning.

Officers from the Metropolitan Police’s counter-terrorism command have launched an investigation following the explosion during rush hour.

The force said police were called at approximately 8.20am to Parsons Green station “following reports of a fire on the train”.

The Met said Deputy Assistant Commissioner Neil Basu said: “At present we are aware of a number of people who have suffered injuries.”

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