May: London attacker was known to the police

May described Wednesday's attack as "an attack on free people everywhere".

In a powerful statement, May said that the terrorist "tried to silence our democracy".

"But today we meet as normal, as generations have done before us and as future generations will continue to do, to deliver a simple message: we are not afraid and our resolve will never waver in the face of terrorism," she told MPs.

Eight arrests have been made in London and Birmingham after the attack that left four dead.

Several people from other nationalities - three French teenagers, two Romanians, two Greeks, four South Koreans, one German, one Pole, one Irish, one Chinese, one Italian, and one American - are amongst around 40 of the injured, as the attacker rammed into pedestrians with a car on Westminster Bridge.

"A terrorist came to the place where people of all nationalities and culture gather to celebrate what it means to be free," May said, paying tribute to the police officer, who tried to stop the knife-wielding attacker at the parliament.

In an emotional parliamentary debate, MPs hailed their fellow lawmaker Tobias Ellwood as a hero. Ellwood gave first aid to the police officer on the scene, Keith Palmer, who later died of his injuries.

May said that the attacker acted alone, and was inspired by "Islamist ideology". She added that the intelligence services do not believe there is an imminent threat of further attacks.

The attacker has not yet been named by British authorities, since the investigation is still ongoing.

The news agency Amaq, used by the Islamic State for propaganda, has said in the meantime that the group claims responsibility for the attack.

Acts of normality

May said the millions of "acts of normality" are the best way to defeat terrorism.

"The greatest response lies not in the words of politicians, but in the everyday actions of ordinary people," May concluded, saying the streets are busy, the cafes are open, and millions continue to travel to London to see "the greatest city on Earth".

Police presence will be stepped up in London, nevertheless.

This terror attack, the worst in Britain since 2005, took place exactly a year after the deadly terrorist bombings in Brussels.

An EU Commission spokesperson expressed sympathy and solidarity with UK.

He added that European Commission president Jean-Claude Juncker will have a phone conversation with Theresa May on Thursday.

In preparations for the Rome summit on Saturday, Italy's interior minister, Marco Minniti, ordered an increase of security, raising the country's security alert to the highest level.

An extra 2,000 police officers will be deployed on the streets of the eternal city, Rome, in addition to the 3,000 already planned.

In Rome, 27 EU national leaders are will arrive – with the exception of May – alongside the heads of the EU institutions to celebrate the 60th anniversary of the signing of the Treaty of Rome.