Prime Minister Theresa May said on Thursday terrorism would not prevail as she rallied the country to carry on with its everyday business and stick to British values in response to an attack on parliament.

“At this time it is so important that we show that it is our values that will prevail, that the terrorists will not win, that we will go about our lives showing that unity of purpose and the values that we share as one nation going forward and ensuring that the terrorists will be defeated,” she told parliament.

Earlier in the day British police raided several properties and arrested seven people in connection with the attack outside Parliament that left four dead, including the man who mowed down pedestrians on a bridge and fatally stabbed an officer, a senior police official said.

Police raided six addresses, including some in the central city of Birmingham, and arrested seven people in connection with Wednesday's attack by a knife-wielding man who also mowed down pedestrians with an SUV on Westminster Bridge, Metropolitan Police counter-terrorism chief Mark Rowley said.

He revised the death toll from five to four, including the attacker, the police officer and two civilians. He said that 29 people required hospitalisation and seven of them are in critical condition. He also said that authorities were still working out the number of “walking wounded.” Police had previously given the total number of injured as around 40.

Rowley said investigation were continuing around Parliament but expected that lawmakers would be able to go ahead with plans to reconvene in a show of solidarity.

A knife-wielding man drove an SUV into pedestrians on Westminster Bridge before crashing the vehicle into the gates of Parliament on Wednesday. He scaled the fences and later fatally stabbed a policeman before being gunned down by officers. He hasn't been identified. Three pedestrians were among the dead.

Prime Minister Theresa May condemned as a “sick and depraved terrorist attack.” Lawmakers, lords, staff and visitors were locked down after the man was shot by police within the perimeter of Parliament, just yards from entrances to the building itself and in the shadow of the iconic Big Ben clock tower.

A doctor who treated the wounded from the bridge said some had “catastrophic” injuries. Three police officers, several French teenagers on a school trip, two Romanian tourists and five South Korean visitors were among the injured.

'International terrorism'

British police say they believe the attacker who killed four people including a police officer outside Parliament acted alone and was 'inspired by international terrorism.' Rowley says that police have raided six addresses and arrested seven people in connection with Wednesday's attack. He refused to identify the attacker.

There was no immediate claim of responsibility.

He said that the death toll stands at five, including the attacker, a police officer guarding Parliament and three civilians. He said that 29 people required hospitalisation and seven of them are in critical condition.

The threat level for international terrorism in the U.K. was already listed at severe, meaning an attack was “highly likely.” Speaking outside 10 Downing St. after chairing a meeting of government's emergency committee, COBRA, May said that level would not change. She said attempts to defeat British values of democracy and freedom through terrorism would fail.

Londoners and visitors “will all move forward together, never giving in to terror and never allowing the voices of hate and evil to drive us apart,” May said.

President Donald Trump was among world leaders offering condolences.

London has been a target for terrorism many times over past decades. Just this weekend, hundreds of armed police took part in an exercise simulating a “marauding” terrorist attack on the River Thames.