Updated

British Prime Minister David Cameron vowed to confront radical Islam "at home and abroad" and the United Kingdom raised its terror level to "severe"  in the wake of new revelations about Islamic State's butchery in Syria and Iraq.

Cameron, speaking from 10 Downing Street, said Britain's problem with homegrown radical jihadists joining the bloody battle engulfing the Middle East and threatening attacks on the west must be addressed with tough action.

"This is not some foreign conflict thousands of miles away that we can hope to ignore," the Conservative Party leader said. "The ambition to create an extremist caliphate in the heart of Iraq and Syria is a threat to our own security here in the UK. And that is in addition to the many other Al Qaeda-inspired terrorist groups that exist in that region. The first ISIL terrorist attacks on the continent of Europe have already taken place."

"We cannot appease this ideology," the Conservative Party leader said. "We have to confront it at home and abroad. To do this we need a tough, intelligent, patient, comprehensive approach to defeat the terrorist threat at its source.

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Cameron's words came one day after U.S. President Barack Obama said the U.S. is not contemplating imminent action against Islamic State in Syria.

"I don't want to put the cart before the horse. We don't have a strategy yet," Obama said Thursday.

International outrage at Islamic State continues to grow with daily reports and images of the terror group's savagery against Syrians, Iraqis and Kurds. On Thursday, video of Islamic State fighters marching more than 100 underwear-clad Syrian soldiers in the desert before summarily executing them appeared on the Internet. On Friday, Islamic State released photos of Kurdish Peshmerga soldiers captured ion Iraq, one of which was beheaded.

The UK government raised its terror threat level from "substantial" to "severe," the fourth highest of five levels, in response to events in Iraq and Syria. The move means a terrorist attack is highly likely, although there is no intelligence to suggest one is imminent, Home Secretary Theresa May said. Cameron noted it was the first time in three years the level was raised to severe by the U.K.'s Joint Terrorist Analysis Center.

"My first priority as Prime Minister is make sure we do everything possible to keep our people safe," Cameron said.

White House Press Secretary Josh Earnest said on Friday the U.S. has no current plant to raise its own threat level.

Earnest also went to great lengths Friday to say the U.S. is not "at war" with Islamic State and the Obama administration has been criticized for not addressing the issue of Islamic extremism explicitly and decisively enough, Cameron said the "root cause" of the terrorist threat in his nation is "Islamist extremism." hundreds and possibly more than 1,000 Britons have gone to Syria and Iraq to join Islamic State, which claims to have established a caliphate, or nation of strict Sharialaw, in Syria and Iraq.

Cameron said plans are being developed to stop British jihadists from traveling to Syria and Iraq and to make it easier to revoke their passports. He also said the nation will work to bar current fighters from returning from the Middle East.

Cameron distinguished between the religion of Islam and the "poisonous" political ideology of extremists.

“We are in the middle of a generational struggle between a poisonous and extremist ideology that I believe that we'll be fighting for years, and probably decades,” he said.