IN a trademark tweet posted within hours of the London Underground blast, US President Donald Trump claimed the perpetrators had been “in the sights” of Scotland Yard – and earned a rebuke from the Metropolitan Police and the Prime Minister.

Trump wrote: “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!”

His intervention threatened to place fresh strain on the US-UK intelligence-sharing relationship which has come under pressure several times since he entered the White House, and triggered social media speculation that he was sharing what he had been told by the UK.

Scotland Yard said Trump’s comments – which did not correspond with any information released by UK authorities – were “pure speculation”.

After chairing a meeting of the Government’s Cobra emergencies committee, Theresa May said it was not “helpful” to speculate on what was an ongoing investigation.

She said police and security services were still working to identify those responsible for the attack on the packed commuter train.

In Downing Street, she said: “I never think it’s helpful for anybody to speculate on what is an ongoing investigation. The police and security services are working to discover the full circumstances of this cowardly attack and to identify all those responsible.”

Asked later if he had been briefed on any intelligence about the attack, Trump appeared to sidestep the issue saying he had been briefed “on numerous things’’, including North Korea.

“It’s a terrible thing. It just keeps going and going, and we have to be very smart, we have to be very, very tough. Perhaps we are not nearly tough enough,” he said.

“It’s just an absolutely terrible thing. In fact, I’m going to call the Prime Minister right now. We have to be tougher and we have to be smarter.”

The latest spat comes after British police temporarily suspended intelligence-sharing with the US in the wake of the Manchester Arena bombing in May, following a series of leaks to American media.

But the “special relationship” had already come under strain earlier in the year, when the then White House press secretary Sean Spicer repeated claims that GCHQ, the UK surveillance agency, had been involved in bugging the Trump campaign on behalf of Barack Obama.

His comments drew a rare public statement from GCHQ denouncing the allegation as “utterly ridiculous”.

One security expert, meanwhile, said British Transport Police (BTP) should be given more resources to boost safety on the Underground.

Deploying more officers should be prioritised over installing check points at Tube stations, according to Will Geddes, founder of private security firm International Corporate Protection.

He said introducing airport-style barriers “is not necessarily going to be a solution” because of the huge number of passengers using the network.

Around Parsons Green, free pizza, cups of tea and spare phone chargers were on offer as well-meaning residents sprang into action following the blast.

West Londoners fastened signs to their front doors telling anyone affected to come if they need anything from a beverage to a toilet break.

At the fringes of the police cordon, Teo Citino, the owner of nearby restaurant Il Pagliaccio, piled a fold-out table with free pizza for the emergency services.

The 52-year-old said: “My wife and daughter could have been on that train, I live next to the station. I rang my wife right away, they were evacuated from the house in pyjamas.

“I must admit, I have been very, very lucky because they usually get the train to go to my daughter’s school.”