LONDON, ENGLAND - JULY 22: British Home Secretary Theresa May speaks at the 'Girl Summit 2014' in Walworth Academy on July 22, 2014 in London, England. At the one-day summit the government has announced that parents will face prosecution if they fail to prevent their daughters suffering female genital mutilation (FGM). (Photo by Oli Scarff/Getty Images) British Home Secretary Theresa May speaks at the "Girl Summit 2014" in Walworth Academy on July 22, 2014 in London, England. (credit: Oli Scarff/Getty Images)

LONDON (WNEW/AP) — Britain raised the terror threat level from substantial to severe Friday, meaning that a terrorist attack is considered highly likely.

Home Secretary Theresa Mays said the decision to raise the threat level was related to developments in Iraq and Syria, but that there was no information to suggest an attack was imminent. Some of the plots are likely to involve fighters who have traveled from Britain and Europe to take part in fighting in the Middle East.

“We face a real and serious threat in the UK from international terrorism,” she said. “I would urge the public to remain vigilant and to report any suspicious activity to the police.”

May says the decision by the Joint Terrorism Analysis Center is made on the basis of intelligence and is independent of government. “Severe” is the second-highest of five levels.

British Prime Minister David Cameron called the Islamic State of Iraq and Syria a “greater and deeper threat to security than we have seen before.”

“We cannot appease this ideology, we have to confront it at home and abroad,” Cameron said Friday.

British police have appealed to the public to help identify aspiring terrorists after the murder of an American journalist focused attention on extremism in the U.K.

The involvement of a person of British nationality in James Foley’s murder underscored the need to identify those who might travel abroad to fight or are at risk of being radicalized.

The warning comes as President Barack Obama said Thursday during a press conference that the administration has yet to develop a strategy to deal with the Islamic State of Iraq and Syria.

“I don’t want to put the cart before the horse. We don’t have a strategy yet,” Obama stated.

White House officials told CBS News that Obama’s remark referred to a specific military strategy for dealing with ISIS.

“I just want to be clear about what our strategy is. The president’s clear in that this strategy is one that’s not going to solve this problem overnight. But he’s also clear about the fact that our strategy can’t only be the American military,” White House Press Secretary Josh Earnest told CNN. “We have a comprehensive strategy for dealing with ISIL. One component of our broader strategy is the use of military force.”

The president is still determining whether or not to conduct airstrikes in Syria to target ISIS. The U.S. has been conducting airstrikes in Iraq against the terror group.

“We need to make sure that we’ve got clear plans so we’re developing them. At that point I will consult with Congress and make sure that their voices are heard,” Obama explained.

Just last week, Joint Chiefs of Staff chairman Gen. Martin Dempsey said that ISIS needs to be confronted in Syria.

“To your question, can they be defeated without addressing that part of their organization, which resides in Syria? The answer is no,” Dempsey said last week during a press briefing at the Pentagon. “That will have to be addressed on both sides of what is essentially at this point a nonexistent border.”

Secretary of State John Kerry will be traveling to the Mideast next week in an effort to coordinate a response against ISIS.

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