Monday. We begin with the growing power of terrorism. Tonight, great Britain raising the threat level to severe. Brian Ross has details on that move, and what American authorities are weighing... See More
Monday. We begin with the growing power of terrorism. Tonight, great Britain raising the threat level to severe. Brian Ross has details on that move, and what American authorities are weighing tonight. Reporter: The urgent british warning came today as this latest Isis propaganda and execution videos circulated on the internet. Here, several hundred men, described as Syrian soldiers, marched across the desert in their underwear before being executed. Part of what the british prime minister today called the poisonous ideology of islamist extremism. What we're facing in Iraq now with isil is a greater and deeper threat to our security than we have known before. Reporter: The british recruits to Isis are considered some of the group's most brutal fighters. In fact, U.S. Negotiators said today a team of Brits not only organized the execution of James Foley, in an Orange prison jumpsuit, but also subjected him and other American hostages to waterboarding, a response to the American treatment of Al Qaeda prisoners. The U.S. Said today it is considering its own enhanced steps because of concerns about the estimated 100 American recruits to Isis. A lot of times, these individuals are fairly adept at covering their tracks. Reporter: Despite the groups' rigid beliefs about all things western, online rap music has become an increasingly popular means of Jihadi recruitment. Listen to this American voice. ? This goes out to all my soldiers, freedom fighters, equalizer ? ? they slaughter us like animals now it's time for that beast to bite them ? ? black flags we worldwide Syria to Atlanta ? Young men being recruited by other young men. Reporter: Authorities say almost a dozen young men have been recruited in a kind of pipeline from the Minneapolis area, and now there is concern that teenage girls from here are also being recruited. These are women living boring lives, believing they're going to bring the end of the world, the rise of the new Cal I have fat. Reporter: This Isis video shows women being trained to fight and community leaders in Minneapolis say one family has reported this week that their 19-year-old daughter has gone to Syria. And my be joining the fight. The Pentagon said it's costing the U.S. About $700 million a day for its limited operations in Iraq. And the coast is about $560 million.
This transcript has been automatically generated and may not be 100% accurate.