LONDON/WASHINGTON (Reuters) – A man arrested on suspicion of planning a terrorist act on Thursday, carrying knives near Prime Minister Theresa May’s office, was on a ship raided by Israeli soldiers in 2010, sources familiar with the investigation have told Reuters.

The 27-year-old man was arrested by armed counter-terrorism officers during a stop-and-search as part of an ongoing security operation, British police said.

No one was injured in the incident and police said knives had been recovered from the man, who was being monitored by British intelligence agents and counter-terrorism officers.

He remains in custody on suspicion of terrorism offences and possession of an offensive weapon.

Sources told Reuters on Friday the suspect was Khalid Omar Ali from London.

Ali was on board the Mavi Marmara, part of a flotilla which was challenging an Israeli naval blockade of the Gaza Strip when it was intercepted by the Israeli Defence Forces in May 2010, the sources, speaking on condition of anonymity, said.

Nine Turkish activists were killed in the raid.

However, one source close to the current investigation said that investigators believed that Ali’s involvement in the boat protest was entirely separate from whatever might have led up to Thursday’s incident.

A man who is identified as Ali also features on a video on an activist’s website from 2010.

In the footage, he states he was among a group who said they were held against their will by the captain of the Greek-managed ship Strofades IV when they tried to take aid by sea from Libya to Gaza some months after the Mavi Marmara incident.

He also talks about joining the Road to Hope convoy which sought to take aid to Gaza in Nov. 2010 via Egypt.

(Reporting by Michael Holden and Mark Hosenball in Washington; editing by Ralph Boulton)