Theresa May rounded on Donald Trump yesterday after he claimed the Parsons Green bomber had been under surveillance by Britain’s security services.

In an extraordinary breach of diplomatic protocol, the US President took to social media within hours of the attack to claim the suspect was ‘in the sights of Scotland Yard’.

He later walked back on his controversial comments, tweeting: 'Our hearts and prayers go out to the people of London, who suffered a vicious terrorist attack.'

Theresa May (pictured in No 10 this afternoon) said any speculation was unhelpful when asked about the President's tweets on the Parsons Green attack

Trump tweeted: '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 later walked back on his controversial comments, tweeting: 'Our hearts and prayers go out to the people of London, who suffered a vicious terrorist attack'

Earlier he 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 comments drew a swift rebuke from the Prime Minister, who said: ‘I never think it’s helpful for anybody to speculate on what is an ongoing investigation.’ She later challenged the president in person when he called her to discuss the case.

A Scotland Yard spokesman also criticised Mr Trump, saying: ‘The comments are unhelpful and pure speculation. If anyone has got any evidence or information, please contact the anti-terrorism hotline.’

Mrs May’s former chief-of-staff Nick Timothy commented on Twitter, saying: ‘True or not – and I’m sure he doesn’t know – this is so unhelpful from leader of our ally and intelligence partner.’

Mr Trump appeared unconcerned about his diplomatic slip. Asked about the terror attack by reporters outside the White House, he said: ‘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. It’s just an absolutely terrible thing. In fact, I’m going to call the Prime Minister right now.

Met terror chief Mark Rowley updated the media on the investigation this morning (pictured) but has not given any details of any man hunt

U.S. National Security Advisor H.R. McMaster (right) told reporters at the White House on Friday that Trump wasn't speaking about any particular terror suspect when he claimed Scotland Yard had already had Friday's Tube bomber on its radar

President Donald Trump has claimed Scotland Yard knew ahead of time about a bomber or bombers who set off a crude incendiary bomb Friday morning on London's 'Tube' subway

‘We have to be tougher and we have to be smarter.’ He told reporters that he had been briefed on the explosion, but did not provide further details.

His national security adviser HR McMaster suggested later that Mr Trump was speaking generally.

HOW RELEASING INFORMATION HELPED CATCH BARCELONA ATTACKER Images of Barcelons suspects Moussa Oukabir and brother Drissa emerged within a few hours of the Las Ramblas attack More than seven hours after the terror attack in Parsons Green, police in London are still refusing to confirm whether they have a suspect. The approach taken contrasts sharply with the response to the last major terror attack in Europe, Barcelona in August. Just over an hour after the attack took place, Spanish police tweeted the public to say they were searching for the attacker and to avoid the area. Then, within three hours after the attack, a photo of a suspect, Driss Oukabir, was released and circulated online. The release of the image caused Oukabir to come forward to his local police and tell officers his documents had been stolen. This was again revealed to the media as Oukabir's younger brother Moussa became the prime suspect. Advertisement

Noting that law enforcement agencies have been working to combat terrorism for years, Mr McMaster said: ‘I think if there was a terrorist attack here, God forbid, that we would say that they were in the sights of the FBI.’

He added: ‘I think he means generally that this kind of activity is what we are trying to prevent.’

The controversy threatened to reopen the row between the UK and the US over the leaking of sensitive police information that led to the temporary suspension of security co-operation in the wake of the Manchester bombing.

Labour MP Stephen Doughty, a member of the home affairs select committee, said last night Mr Trump’s intervention ‘has the potential to not only undermine a vital relationship, but also to prejudice investigations into this and other incidents’.

Liberal Democrat home affairs spokesman Sir Ed Davey said: ‘It is insulting to the victims of this attack that Donald Trump is already using it to try and further his divisive political agenda. Once again, Trump has shown he is not fit for the office of US President.’

London Mayor Sadiq Khan, who clashed with Mr Trump over his response to the London Bridge terror attack, would not be drawn on the president’s comments. ‘I’ve simply been too busy to look at my Twitter,’ he said. ‘My priority is making sure that we do what we can to keep Londoners safe.’

A City Hall source said: ‘He hopes people don’t speculate on things before we know the full facts. It’s clear what he thinks about that.’

In May, British police temporarily suspended intelligence sharing after a series of damaging US leaks about the investigation into the Manchester bombing.

Images of the remnants of terrorist Salman Abedi’s backpack and a diagram showing where his victims died were handed to a US newspaper.

Trump added: '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!'

Theresa May's former adviser Nick Timothy reacted to Trump's intervention by saying the president 'doesn't know' anything: 'This is so unhelpful from leader of our ally and intelligence partner'

Metropolitan Police officers were continued detailed searches and investigations at the scene of the bombing today (pictured)

The Prime Minister tackled Mr Trump over the issue at a Nato summit in Brussels, telling reporters later that the ties between Britain and the US were the ‘deepest defence and security partnership we have’, but warned it was ‘built on trust’.

She added: ‘Part of that trust is knowing that intelligence can be shared confidently and I will be making clear to President Trump that intelligence that is shared between law enforcement agencies must remain secure.’

Britain and the US are key members of the so-called ‘Five Eyes’ intelligence-sharing community, which also includes Australia, Canada and New Zealand.

Police in and around London are hunting for the 'bucket bomber' who tried blow up a rush hour Tube train amid claims that he is armed and may have left other devices

The crude device could have killed dozens but failed to properly detonate and sent a 'wall of fire' through a subway car, injuring at least 22 people including a ten-year-old boy

The latest version of Trump's travel ban, initially announced in a botched late-January rollout, calls for a ban on people entering the U.S. from six terror-prone countries that are also Muslim-majority nations.

It also bars the entry of most refugees from anywhere in the world.

Federal court challenges have resulted in exceptions being made for travelers who already have established ties to the U.S., including a broad definition of what counts as a close family member.

The U.S. Supreme Court is expected to hear oral arguments to decide the ban's constitutionality in October, but allowed it to go into effect last month while the case is pending.

Police in and around London hunted Friday for a 'bucket bomber' who tried to blow up a rush hour Tube train amid claims that he is armed and may have left other devices.

The crude device could have killed dozens but failed to properly detonate and sent what was described as a wall of fire through a subway car, injuring at least 22 people including a ten-year-old boy.

The president linked Friday's attack to his controversial travel ban, saying it 'should be far larger, tougher and more specific – but stupidly, that would not be politically correct!'

He also drew attention to the military action against ISIS and should the US should get 'nasty'

Terrified passengers ran for their lives and were seen covered in blood with scorched hands, legs, faces and hair after the incident in west London during the morning commuting rush hour.

Photographs from the District Line train show what experts believe is a 'pretty unsophisticated' bomb in a flaming white bucket inside an insulated freezer bag bearing the logo of the 'Lidl' European grocery chain.

Christmas tree lights are also shown connected to a battery protruding out of the top.

Witnesses said there was a loud 'bang' and a flash – and then a ball of flame engulfed surrounding passengers.

Scotland Yard said it was a terror attack but would not officially confirm claims that there is another device or that a suspect is on the run.

But an officer at the scene told MailOnline: 'We believe there is a second bomb – there is a man with knives on the loose.'

Luke Warsmey said the explosion was like a 'giant match' sparking and he saw a woman with no skin on her legs and a ten-year-old boy with a burned body.

He said: 'People just started sprinting. It was sort of every man for himself when that happened. The burn victims had severe leg injuries.

'It was a very busy commuter train, young and old, school children going to their schools. I saw was nannies trying to look for kids, because of the rush of people just taking five- and six-year-olds away from them and they were trying to look for them.'