Flowers are laid at the scene after an attack on Westminster Bridge in London, Britain, March 22, 2017.  [Photo/Agencies]

Britain has been on high alert for several years. Its security services monitor about 3,000 individuals, many of whom have fought in Syria, Afghanistan, Somalia, Libya or Yemen. Sources said Masood did not feature in that list.

The security services are expected to track down the assailant’s associates and those he communicated with and check on the places he visited before the attack.

Officials said Masoodlikely acted alone, but may have been inspired by communications from abroad.They are particularly focused on the Islamic State in Iraq and Syria and different branches of al-Qaida.

The police officer who was killed was identified as Police Constable Keith Palmer, a 48-year-old father of two.

AyshaFrade, 43, a mother of two, who worked as a teacher in London but came from the Spanish town of Betanzos in Galicia, was killed on Westminster Bridge.

The third victim was named as Kurt Cochran, 54, from Utah in the United States, who was in London to celebrate his 25th wedding anniversary.

Those injured included 12 Britons, three French schoolchildren, two Romanians, four South Koreans, two Greeks and one person each from China, Germany, Poland, Ireland, Italy and the US.

Three off-duty police officers were hurt, two seriously.

Hua Chunying, a spokeswoman for China’s Foreign Ministry, confirmed that a Chinese tourist suffered minor injuries in the attack.

Wednesday’s incident was the latest in a series of attacks committed for political and religious reasons in Britain. Most were committed by Islamists, but at least two murders were carried out by far-right extremists, including the killing of Jo Cox, a member of Parliament who was killed last year before the referendum on Britain’s future with the European Union.