‘This Week’ Transcript: The ISIS Threat to the West

August 31, 2014— -- Below is the rush transcript of "This Week" on August 31th, 2014. It may contain errors.

ANNOUNCER: Global terror alert: the UK sounding the alarm

DAVID CAMERON, BRITISH PRIME MINISTER: Increased the threat level to severe.

ANNOUNCER: Warning an attack is highly likely. What has authorities so worried?

Plus, more Americans signing up to join the jihadist army. Who are these recruits? And why are they now targeting teenaged girls? This morning, breaking developments from our team around the globe.

Then, are you ready for some football? The NFL commissioner admits a mistake. Does the league's new domestic violence policy go far enough?

And we're teaming up with Facebook, tracking the stories you're turning into trends. Time to reveal our first Facebook find of the week.

From ABC News, This Week with George Stephanopoulos begins now.

MARTHA RADDATZ, HOST: Good morning, I'm Martha Raddatz.

There are fast moving developments in the battle against ISIS, including a breakthrough for the Iraqi army against the terror group as the U.S. launches another round of airstrikes and humanitarian drops.

Plus, new fears just 48 hours after the UK warned an attack there is highly likely. We're covering every angle this morning. Let's start off with ABC's senior justice correspondent Pierre Thomas. Good morning, Pierre.

PIERRE THOMAS, ABC NEWS CORRESPONDENT: Good morning, Martha.

Threat level severe, likelihood of a terrorist attack high, that's the blunt British assessment.

(BEGIN VIDEOTAPE)

THOMAS: In Great Britain, signs of stepped up police patrols, hard evidence that the Islamic radicals terrorizing parts of Iraq and Syria are a direct threat to the UK, the U.S., indeed all of the west.

CAMERON: This is not some foreign conflict thousands of miles from home that we can hope to ignore.

THOMAS: According to U.S. intelligence, and estimated 12,000 foreign fighters have gone to Syria, more than 100 from America, but 1,000 from Europe.

CAMERON: And you're dealing not just with ISIL, you're also dealing with other al Qaeda-linked franchises in Syria and indeed potentially in Iraq.

So that's the reason for the threat level change.

THOMAS: American intelligence sources say they've identified no specific plots, but British authorities are likely responding to chatter from radicals in Syria and Iraq talking about targeting England, radicals whose travel documents give them easy access to Europe and the U.S. are the most urgent threats.

Just in recent months, an American blowing himself in Syria, another dying on the battlefield fighting alongside ISIS, a Brit beheading American journalist James Foley -- a Syria-based threat that top U.S. officials have been warning about for months now tangible.

Homeland security secretary Jay Johnson.

JEH JOHNSON, HOMELAND SECURITY SECRETARY: Syria has become a matter of homeland security.

THOMAS: The FBI director.

LOUIS FREEH, FBI DIRECTOR: They're coming back. They're coming back to Europe, they're coming back to North America.

THOMAS: Attorney General Eric Holder.

ERIC HOLDER, U.S. ATTORNEY GENERAL: It's more frightening than anything I think I've seen as attorney general.

THOMAS: We caught up with Holder in London as he was sounding the alarm with his European counterparts.

How concerned should Americans at home be about ISIS.