Conservative MP James Cleverly has paid tribute to PC Keith Palmer whom he had known for 25 years.

The nationalities have emerged of some more of those injured in the attack outside Parliament. Five South Korean tourists were injured, one of them seriously, a tour agency official told the Yonhap news agency. , external

The South Korean tourist with a serious injury was identified as a 67-year-old woman, the agency said, adding that she was being treated at St Mary's Hospital. 

Mr Rowley also said in the news conference: "The UK threat level has been at 'severe' for some time and this level will not change.

"We have enhanced the scale of the policing operation to protect our communities across the country.

"As we continue to investigate today's horrific events we do want to reassure the public that police and partners are doing everything possible to protect them.

"As a precautionary measure over the next few days we have increased the number of officers on duty to provide a highly visible, reassurance presence - both armed and unarmed - across the country."

Mark Rowley, the national lead for Counter Terrorism Policing and the Acting Deputy Commissioner, said: "Terrorists have a clear aim and that is to create discord, distrust and to create fear.

"The police stand with all communities in the UK and will take action against anyone who seeks to undermine society, especially where their crimes are motivated by hate. 

"We must recognise now that our Muslim communities will feel anxious at this time given the past behaviour of the extreme right wing and we will continue to work with all community leaders in the coming days.

"It's essential for us to remain vigilant but to also work together - policing and communities - and unite against those who seek, through violence and extremism, to threaten, intimidate and cause fear."

Mark Rowley said in the news conference that police believed the attacker was inspired by international terrorism.

Keith Palmer, 48, had 15 years service as a police officer and was killed in today's attack, police have confirmed.

Image source, PA

Eleanor Garnier
Political Correspondent

Image source, PA

Theresa May came out into Downing Street tonight to tell the world that any attempt to defeat the values that Parliament stood for was "doomed to failure". 

She said the streets of Westminster, where the attack took place, were engrained with a spirit of freedom that echoed in some of the further corners of the globe.  

Praising the police and security services for their exceptional bravery she said the fact that they had lost one of their own today only made their calmness and professionalism under pressure all the more remarkable.  

Parliament had been packed at the time of the incident with politicians, tourists and school children too. It was quickly cordoned off as medics and emergency services arrived.  

Westminster went into lockdown and some MPs were held in the Commons chamber, Others were moved to Westminster Abbey for safety.  

As politicians left this evening they spoke of their shock and sadness and praised the police officer who lost his life protecting politicians and parliament. The best and the bravest, one MP said.

Flags are to be lowered to half-mast over Downing Street as a mark of respect to the people who died.

The officer who died in the attack has been named as Keith Palmer.

Scotland Yard's Mark Rowley said Mr Palmer, 48, had 15 years service as a police officer and was a husband and father.

He said he would not comment on the identity of the attacker, although he suggested the police was aware of who the alleged assailant was. 

Scotland Yard's top anti-terror officer Mark Rowley confirms that five people have died and about 40 people were injured in the attack, including three police officers. 

At 14.40 (GMT) the Metropolitan Police were called to an incident around Parliament Square in central London.

Reports made to the police included a person in the river, a car hitting pedestrians and a man armed with a knife

Witnesses saw a car drive across Westminster Bridge and hit a number of pedestrians walking on the pavement.

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