London: About 800 Islamist extremists recruited by Islamic State or groups affiliated to the al Qaeda are preparing to launch attacks in Europe, according to a media report.
The Islamist fighters who have returned from Syria or Iraq are preparing to launch attacks in Europe, The Times reported citing Spanish counterterrorism officers.
The Spanish officers referred to the number of jihadists residing on the continent who have been recruited by Islamic State or groups affiliated to al-Qaeda.
Another 350 or so Britons have returned from fighting in the war zone, with security sources acknowledging that some are plotting attacks in the UK specifically.
The warnings come after Ayoub El Khazzani, 25, a Moroccan gunman, was overpowered on a high-speed train travelling from Amsterdam to Paris on Friday. He was said to be an "Islamist returner," apparently having left France for Syria last year.
Counterterrorism sources quoted by Cadena Ser, a Spanish radio station, said about 800 extremists on the continent had been recruited by Islamic State or al-Qaeda-affiliated groups.
They said they were waiting for instructions from support networks to commit atrocities when the opportunities arose.
The sources were quoted as saying that they believed El Khazzani had been armed and given instructions by others before boarding the train, and discounted his claim that he was trying to carry out a robbery and was not a terrorist.
Anti-terrorist sources said they were tracking the movements of some of the 800 "returners", but did not know the whereabouts of all of them.
All have returned from conflict zones and are awaiting their opportunities to carry out an attack, they said.
"These people are not well trained, but they are poised and prepared to do anything. Once they have been indoctrinated, they receive the minimum training," the radio station's unnamed source said.
More than 700 Britons are thought to have travelled to Syria and Iraq to support or fight for jihadist organisations. According to Scotland Yard, half of them have returned.
Police and the security services are monitoring a fraction of the returnees, while others have been referred for action under Prevent, the counter-extremism strategy.
Some are thought to be planning attacks in the UK, while some have encouraged others to go to the war zone, or raised funds for them.
The number of people arrested for Syria-linked terrorism offences rose by 560 per cent in 12 months. A total of 165 arrests were made across the country last year, compared with 25 in 2013.
The terrorist threat level remains severe, meaning that an attack is highly likely.
Francisco Mart?nez, Spain's security minister, said last week: "These young men are so quickly converted to support Islamic State, and in a few weeks they become fanatics. They go to war zones or they stay where they live and act like lone wolves."