The Islamic State group have on Thursday claimed responsibility for an attack by a man who drove an SUV into pedestrians on a crowded London bridge and then stabbed a police officer to death on the grounds of Britain's Parliament.

The Islamic State group said through its Aamaq News Agency that the attacker was a soldier of the Islamic State who "carried out the operation in response to calls for targeting citizens of the coalition" of countries fighting IS in Syria and Iraq.

The IS group has been responsible for numerous bloody attacks around the globe and has specifically called for Western followers to carry out this kind of attack in their own countries, though the group has also claimed attacks later found to have no clear links to it.

May set an unyielding tone Thursday in a sweeping statement before the House of Commons. While she honoured the police, she also saluted the actions of millions of people who went about their lives as normal, describing it as proof that the act of terror failed.

"As I speak millions will be boarding trains and airplanes to travel to London, and to see for themselves the greatest city on Earth," she told the House of Commons. "It is in these actions - millions of acts of normality - that we find the best response to terrorism —a response that denies our enemies their victory, that refuses to let them win, that shows we will never give in."

Parliament began its moment of silence at 9:33 a.m., honouring the shoulder number of the murdered officer, Keith Palmer, a 15-year veteran of the Metropolitan Police and a former soldier. Then Parliament, which was locked down after the attack, returned to business — a counter to those who had attacked British democracy.

"Those who carry out such wicked and depraved acts as we saw yesterday can never triumph in our country and we must ensure it is not violence, hatred or division but decency and tolerance that prevails in our country," Trade Secretary Liam Fox said.