Breaking news as we come on the air tonight. American forces on the attack. The first wave of U.S. Air strikes hitting I.S.I.S. Targets in Syria, opening a new front in the battle against the islamic... See More
Breaking news as we come on the air tonight. American forces on the attack. The first wave of U.S. Air strikes hitting I.S.I.S. Targets in Syria, opening a new front in the battle against the islamic terror group. For the very latest, we turn to ABC's chief global affairs correspondent, Martha Raddatz. Reporter: Juju, this is the biggest wave of air strikes we have seen in a single day since the U.S. Began attacking I.S.I.S. In early August. And we did not do it alone. Five Arab nations joining in the strike, which pounded some 20 targets in the area of raqqa. That's an??ymp I.S.I.S. Stronghold, and believed to be where the british and Americans were executed. The air strikes carried out by U.S. Stealth bombers and fighters, and tomahawk missiles launched from the sea. The f-22 raptor and expensive stealth fighter used for the first time in combat. The targets, I.S.I.S. Safe havens. Command and control and logistic centers. Twitter, lit up with reports of huge explosions around raqqa. The other Arab nations taking part, all largely Sunni, including Jordan, Saudi Arabia, Bahrain, Qatar, and the united Arab Emirates. The kind of coalition the U.S. Has been trying to build to go after I.S.I.S. A big step as the U.S. Expands the fight against I.S.I.S. Into Syria, where the president was loathed to go for so long. But he gave the go ahead for these strikes. And throughout this evening, he has been briefed on the progress. Tomorrow, he heads to New York and the U.N. We do expect to hear from him then. These air strikes will be ongoing. The chairman of the joint chiefs of staff says the fight against I.S.I.S. In Syria will be persistent and sustainable, which means this will likely continue for months on end. Juju? Martha, thanks, as always. And joining me now, ABC news chief investigative correspondent, Brian Ross, who has been tracking the growing terror threat. Now, that U.S. Air strikes are under way, what might this mean for I.S.I.S.? This is a ruthless group, whose members seem to enjoy their medieval barbarism. The air strikes led to beheadings. I.s.I.s. Escalated its threats to America, in anticipation of what happened tonight. As I.S.I.S. Turned up the tempo on its propaganda machine today, with new videos of its military-like formations, and dire threats to American civilians, U.S. Officials revealed details of a crackdown on westerners who want to join I.S.I.S. Or already have, like these brittons, who appeared in a new video today. We are working closely with our international partners to mitigate this threat. Reporter: U.s. Officials said today, efforts to shut down the jihad pipeline to I.S.I.S., will focus on Boston, Minneapolis, and Los Angeles. Cities that have already sent a number of young recruits to I.S.I.S. Basic training. The kind of young men and women, seen in this latest video, parading in uniform, with brand-new ak-47s. The urgency of the coming white house push against I.S.I.S., was underscored today by one of the terror groups weekend propaganda messages. Its chief spokesperson earned supporters around the world. If you can kill a disbelieving American or european, especially the spiteful and filthy French, or an Australian or a Canadian, then rely upon Allah and kill him however it may be. And I.S.I.S. Followers posted this video, of a 55-year-old French citizen, they said they had kidnapped and would behead in 24 hours, unless the French stopped bombing of I.S.I.S. Positions in Iraq. As for I.S.I.S. Itself, it is believed to be holding some 15 western hostages, including two, young Americans, all of whom have been threatened with executions. Juju? Brian, is it possible that the air strikes cover for a possible rescue mission? Reporter: That's possible. But U.S. Authorities said if there was any chance, they would try to mount a second attempt. They are looking for command and control centers. This is the first step in a major campaign. Thanks for that update. We turn to Alex Marquardt, who spent the day talking with refugees, fleeing the threat of I.S.I.S. He's just across the border from Syria and joins us from Turkey, where there was a mass exodus under way even before tonight's air strikes. Alex? Reporter: Good evening, juju. The past several days have seen I.S.I.S. Pushing into northern Syria, taking over predominantly kurdish towns. That's sent refugees across the border into Turkey. The U.N. Says 130,000 over the past 4 days. That's the biggest-single exodus of refugees since this war began over 3 1/2 years ago. We met many of the refugees who told us, if they stayed behind, they would have been executed by I.S.I.S. They came with what little they could carry. And angrily told us that the U.S. Is doing nothing to stop the I.S.I.S. Advance. That is before these air strikes started. Many of the refugees in Turkey will be happy to see the air strikes carried out by the U.S. And the other countries. At the same time, it could set off a new wave of refugees, fleeing from safety, from those areas where I.S.I.S. Is operating. The U.N. And Turkey, already preparing for many more refugees to cross the border. Juju? Alex, thanks. Our thanks to Alex Marquardt, reporting from the region. Stay tuned. ABC news for all of the latest on these breaking developments.
This transcript has been automatically generated and may not be 100% accurate.