Scotland Yard sees terror threat as hundreds of Britons return from Syria

As if it were not bad enough that hundreds of radicalized Britons have traveled to Syria to join ISIS, the even worse news for the UK is that hundreds of them have come back.

Such was the information released Thursday by Scotland Yard, London's Metropolitan Police Service. A senior police official said the trend raises the specter of more ISIS-like crimes being committed on home soil.

"There is no doubt of the horrific nature of the offenses being committed overseas," Assistant Commissioner Mark Rowley said. "The influence of those who wish to bring similar violence to the streets of the UK has been an increasing threat here."

According to Scotland Yard, about 700 extremists are believed to be among the many Britons who have traveled to Syria, a significant proportion of whom went there to join the terrorist group ISIS, which has become known for beheading captives in Iraq and Syria in its effort to found a Middle East caliphate.

Terrorism arrests up 33%

In the last year, terrorism-related arrests inside the UK have risen -- up to 338 between April 2014 and March 2015, an increase of 33% over the year before, according to Scotland Yard.

"The type and level of the threat is complex and ranges from lone actors intent on carrying out crude and violent attacks to sophisticated networks set on completing ambitious and coordinated plots," Rowley said.

Historic sites damaged by ISIS 11 photos

EXPAND GALLERY

He urged the public to be vigilant and to report anything suspicious. And he left no doubt that he perceives the threat to be global.

"ISIL and other terrorist groups are trying to direct attacks in the UK," Rowley said, referring to ISIS by an another name, "encouraging British citizens to travel to Syria to fight and train, and are seeking, through propaganda, to provoke individuals in the UK to carry out violent attacks here."

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