The man who killed three people including a police officer and injured dozens more in an attack outside the British Parliament before being shot to death by police was "a peripheral figure" in British terrorism investigations who had a long criminal history that included violent crimes, authorities said Thursday.

The Islamic State group claimed the British-born suspect, identified as Khalid Masood, 52, as one of its "soldiers," reports the Los Angeles Times .

He is believed to be the assailant who plowed through pedestrians on Westminster Bridge on Wednesday, then ran toward the Parliament compound with a knife, which he used to fatally wound Police Constable Keith Palmer before he was shot and killed by other police.

Four people died in the rampage, including PC Palmer and Masood, and 40 others were injured, some seriously. Among the dead was a Utah man who was in London celebrating his 25th wedding anniversary with his wife.

The assailant appeared to have acted alone but was inspired by Islamist-related international terrorism, said Mark Rowley, acting deputy commissioner at London's Metropolitan Police. There was no information to suggest there were further threats to the public at this time, police said.

Tobias Ellwood, the Foreign and Commonwealth Office minister, had administered CPR to PC Keith Palmer as he lay on the sidewalk, but could not revive him.

Palmer was a husband and father who had "devoted his life to the service of his country," British Prime Minister Theresa May said.

He was unarmed and standing guard within carriage gates, a courtyard that is not accessible to the public and leads directly into the Houses of Parliament, when the attacker approached him with a large knife and stabbed him several times.

"He was every inch a hero and his actions will never be forgotten," the prime minister said of Palmer.