ISIS Wants To Carry Out 'Enormous And Spectacular' Attacks, British Police Warn

London Metropolitan Police Assistant Commissioner Mark Rowley said the threat from the group which has taken over large parts of Syria and Iraq was evolving, and that it was keen to repeat elsewhere incidents such as last year's Paris shootings and suicide attacks that killed 130 people.

"What we are now seeing in recent months ... is the broadening of that threat, more plans to attack Western lifestyle ... going from that narrow focus on police and military and symbols of the state to something much broader," Rowley told reporters.

"You see a terrorist group that has big ambitions for enormous and spectacular attacks, not just the types that we've seen foiled to date."

British security chiefs have previously warned that the biggest threat posed by the group was the radicalization of young Britons over the internet and the danger posed by those who joined the fighting in Syria and Iraq to return home to carry out attacks.

About 800 British citizens are thought to have traveled to Syria, many to join Islamic State (IS), since the outbreak of civil war.

Rowley said recent arrests showed that IS was adopting a different methodology in trying to get fighters into northern Europe who had weapons and paramilitary training.

"Terrorist groups have always wanted to do the grand and the more spectacular attack because it gets more impact," he said.

He said British police had made more counter-terrorism arrests in 2015 than in any previous year including a marked number of women and those aged under 20.