READING (England) • A man held on suspicion of stabbing three people to death in a British park over the weekend was on the radar of the country's domestic security agency MI5 last year, a security source said.

According to intelligence reports, the man had aspirations to travel for extremist purposes, although his plans then came to nothing.

The Western security source, speaking on condition of anonymity, told Reuters that the suspect was a 25-year-old Libyan named Khairi Saadallah.

British media said Saadallah fled the civil war in Libya and had been released from prison earlier this month, after serving time for a series of non-terror offences.

Mr Mark Rowley, a former assistant commissioner for specialist operations in the Metropolitan Police, said Saadallah would have been one of thousands of people on MI5's watch list.

Some 3,000 people are under investigation at any one time, but there are up to 40,000 people who have come up on the radar in relation to extremist ideology, he told BBC Radio.

"To spot one of those who are going to go from a casual interest into a determined attacker... is the most wicked problem that the services face," he added.

Three people were also hospitalised after the man, wielding a 13cm knife, went on the rampage in the park last Saturday, randomly stabbing people.

Calling the incident terrorism, the police said a 25-year-old had been arrested and that they were not hunting others.

"What we saw here on Saturday evening in Reading were the actions of one lone individual," said Home Secretary Priti Patel.

The Philadelphia Inquirer reported that one of the dead was American citizen Joe Ritchie-Bennett, 39, who had been living in Britain for 15 years.

US Ambassador Woody Johnson sent condolences to the victims' families. "To our great sorrow, this includes an American citizen," he said on Twitter.

Teacher James Furlong, 36, who was friends with Mr Ritchie-Bennett according to media reports, was also killed.

"He was beautiful, intelligent, honest and fun," his parents said.

The third victim has not yet been identified.

Shocked residents of Reading, a town about 65km west of London, held a minute's silence yesterday morning for the victims.

The attack was reminiscent of some recent incidents in Britain that the authorities have also called terrorism.

In February, the police shot dead a man who had stabbed two people on a busy street in London. He had previously been jailed for promoting violent Islamist material.

Last November, another man who had been jailed for terrorism offences stabbed two people to death on London Bridge before he too was shot dead by the police.

REUTERS, AGENCE FRANCE-PRESSE