German Chancellor Angela Merkel has sent a message of support to the people of London
Three people including a police officer were killed by a terrorist who ploughed his car into crowds of pedestrians before launching a knife attack on officers at the Houses of Parliament.
The attacker was then shot by armed police and later died from his injuries.
Mrs Merkel said: "In these hours of sympathy and solidarity our thoughts are with our British friends and all the people in London.”
“My thoughts are especially with the injured to whom I wish a speedy recovery.
"In the fight against any form of terrorism we firmly and decidedly stand by Great Britain."
A union flag flies at half mast above the Palace of Westminster
In these hours of sympathy and solidarity our thoughts are with our British friends and all the people in London
German Chancellor Angela Merkel
Germany suffered a spate of terror incidents last year including the Berlin Christmas Market attack on December 19 when failed Tunisian asylum-seeker Anis Amri.
killed 12 people and left 56 others injured when he ploughed a hijacked lorry into crowds of shoppers.
Minister for Foreign Affairs and Vice Chancellor Sigmar Hartmut Gabriel described the terror attack as ‘an attack on the heart of democracy’.
He said: “It was probably no coincidence that this attack happened close to the Parliament. It was an attack against us all".
Get Quotes on Home Insurance
An armed police officer on patrol in Westminster as security across the capital is stepped up
German president Frank-Walter Steinmeier said: "The news about the murderous attack in London unsettle me.
“My thoughts are with the victims and injured and of with those who are mourning a close person or have to fear for someone.”
Italian Prime minister Paolo Gentiloni said: "Italy is close to the people and the government from Britain facing the attack that struck the heart of London and its democratic institutions.
“I express the condolences of the Italian government and mine to the families of the victims and also my affection to the injured.
“Italy and the UK are side by side in the condemnation and firm response against all forms of terrorism."
Westminster Bridge remains closed after the London terror attack
Italian president Sergio Mattarella has also set a message of condolence to the Queen.
He wrote: “In the fight against all forms of terrorism, the United Kingdom can count on the firm commitment of Italy, in the belief that international co-operation will continue to be a vital aspect to effectively combat violence and intolerance.
“I wish to express, on behalf of all Italians and myself, affection and closeness to the victims' families, to the many wounded and to our friends, the British people."
Spanish prime minister Mariano Rajoy said: “Spain is with the British people. I condemn the attack on Westminster, London. Solidarity with the victims.”