Americans Held Hostage by Al Qaeda We begin with story still unfolding at this hour. Details pouring in. A hostage crisis, american workers kidnapped by an extremist group believed to be linked to al qaeda. It happened in algeria, and tonight, abc's chief global affairs correspondent martha raddatz is traveling with the defense secretary, who is in italy watching every move. Martha? Reporter: Good evening from rome, diane, where defense secretary leon panetta is urgently trying to get more information about this attack on americans and others. Three americans are believed to be held hostage right now, but u.S. Officials warn that number is fluid. Secretary panetta tonight says the u.S. Will take all necessary steps to deal with this crisis. By all indications, this is a terrorist act. And the united states strongly condemns these kinds of terrorist acts. It is a very serious matter when americans are taken hostage along with others. Reporter: It all began when 20 armed islamic militants, believed to be affiliated with al qaeda, approached a group of oil workers. The attackers were reportedly heavily armed, driving in three unmarked vehicles. The oil workers were on a bus headed to a nearby airport. There was a fight -- security forces for the workers battled back. When the smoke cleared, at least one foreign worker was dead, others wounded. The terrorists then headed to the compound where the gas refinery workers live. While it is unclear how many foreign workers they seized, sources say it could be as many as 15 to 20. Along with the americans are british, norwegian, french and japanese workers, too. The attackers claim this is retaliation for the french-led invasion in the african nation of mali. The french are trying to stop an al qaeda-linked group from taking over that country. Algerian troops have surrounded the gas field where the hostages are being held, but they are moving cautiously. Secretary panetta tonight compared the terrorists to 9/11 attackers who have little regard for innocent lives. All right, thank you, martha. But this is new, this is different. I want to bring in abc's brian ross, he's been following the group implicated in this. Brian? Reporter: There are claims by responsibility by an al qaeda group run by mokhtar belmokhtar, who was kicked out of al qaeda last year. So, he was kicked out of al qaeda -- Reporter: Kicked out. And he has the nickname of mr. Marlboro. He carries cigarettes, diamonds, guns and drugs and made millions of dollars kidnapping westerners. So, it's not just ideology, it's about money. Was he on the u.S. Radar? Reporter: Not that we could see. But we've been told for years now to watch out for this man, because he accumulated such wealth, it makes him a real threat to carry out these kinds of attacks. Again, the news is breaking right now, and I know you'll continue to have details online and throughout the evening. Thank you, brian.