Latest: Westminster attack claims fourth civilian with death of 75-year-old man
A 75-year-old man who was injured in the Westminster terror attack has died in hospital, Scotland Yard said.
This brings the death toll of the Westminster attack to five.
Detectives investigating the terrorist attack in #Westminster can confirm that a 75yo man died tonight after his life support was withdrawn.
— Metropolitan Police (@metpoliceuk) March 23, 2017
The Taoiseach has offered his condolences to Prime Minister May this evening.
The two shared a ten minute phone-call this evening - during which Enda Kenny offered any assistance that maybe required as the UK comes to terms with the tragedy.
Britain's Foreign Secretary has led a minute's silence for London's Westminster victims, at the opening of a UN Security Council meeting in New York.
UK police and intelligence agencies mounted a massive investigation to piece together the movements of Khalid Masood in the lead-up to the attack.
Searches were carried out at three addresses in Birmingham and one each in east London, Brighton, south east London and Carmarthenshire
A 39-year-old woman was arrested in east London while a 21-year-old woman and a 23-year-old man were held at one address in Birmingham
A 26-year-old woman and three men aged 28, 27 and 26 were arrested at another address in Birmingham
They were all held overnight while a 58-year-old man was arrested this morning at a third address in Birmingham
Investigators are working on the basis that the attacker acted alone
Car firm Enterprise confirmed the Hyundai used in the attack was one of its vehicles
Islamic State claimed the killer was one of its "soldiers"
A review of security arrangements at Westminster was launched
The Prime Minister addressed MPs as they gathered at the usual time inside the Palace of Westminster.
In a defiant message to a packed House of Commons, Mrs May said: "We will never waver in the face of terrorism."
Paying tribute to Pc Keith Palmer, who died after being stabbed, she said: "He was every inch a hero and his actions will never be forgotten."
The officer's family described him as "brave and courageous", saying his friends and relatives are "shocked and devastated".
The identities of the terrorist's victims on Westminster Bridge have emerged, one a US tourist from Utah celebrating his wedding anniversary, the other a "highly regarded and loved" member of college staff.
Kurt Cochran and his wife, Melissa, on the last day of a trip celebrating their 25th anniversary, were visiting her parents, who are serving as Mormon missionaries in London. Mrs Cochran was badly injured.
Aysha Frade, who worked in administration at independent sixth-form school DLD College London, in Westminster, is understood to have been 43 and married with two daughters.
Meanwhile, Islamic State made its first public pronouncement since the atrocity, claiming in a statement: "The attacker yesterday in front of the British Parliament in London was a soldier of the Islamic State executing the operation in response to calls to target citizens of coalition nations."
Commentators pointed out the terror group has a record of opportunistically claiming attacks and said it was significant the statement did not appear to claim it had directed the strike.
A minute's silence was held nationwide at 9.33am, including in the Palace of Westminster and at New Scotland Yard, to commemorate the three innocent people who were killed.
Forty other people were injured in the attack, with 29 treated in hospital, where seven remained in a critical condition on Thursday.
Five people remained in a critical condition on Thursday evening, two with life-threatening injuries.
The casualties included 12 Britons, three French children, two Romanians, four South Koreans, two Greeks, and one each from Germany, Poland, Ireland, China, Italy and the United States.
Three police officers were also hurt, two of them seriously.
There was a visible police presence at an address in the Olympic Park in Stratford, east London.
A police van was parked outside a building bearing a plaque that read: "During the 2012 summer Olympic and Paralympic Games this building formed part of the Athlete's Village and was home to competitors, coaches and officials from: Benin, Hungary, Israel, Japan, Mali, Sudan."
Plain clothes officers were also seen entering and leaving a block called Lucia Heights.
