U.S. officials have linked the decision to launch an air offensive in Syria not only to the threat Islamic State militants pose to the region, but to the Khorasan group, an al Qaeda offshoot that has until now remained under the radar but which was purportedly in the final stages of planning an attack against the West.

U.S. officials said Tuesday that American forces led coordinated airstrikes on the Islamic State group in the group’s de-facto capital of Raqqa and attacked the Khorasan group in the northeast province to disrupt an imminent attack.

"We believe the Khorasan group was nearing the final stages of an attack in Europe or the homeland," Gen. William Mayville, the Joint Staff director of operations, said at a Pentagon briefing Tuesday. "It is clearly not focused on either the Assad regime or the Syrian people."  

The airstrikes targeted training camps, explosives production facilities, and other command and control facilities, U.S. officials said. 

For weeks, Obama and his advisers have been in discussion with world leaders about joining an international coalition to fight ISIS. Weeks of negotiations led to an eventual partnership, and the president announced Tuesday Jordan, Saudi Arabia, Bahrain, the United Arab Emirates and Qatar are participating in, or supporting, the airstrikes in Syria. Now, that coalition is not only fighting ISIS, but also the Khorasan group.

Syrian activists told International Business Times they were unaware of the Khorasan group; one, from Raqqa, said he only heard of the group from the media coverage Tuesday.

“Nobody knows about this group,” said Qusai Zakarya, a Syrian activist affiliated with a nonprofit organization that advocates for the moderate opposition. 

“Nobody that I know or that I talk to in many areas in Syria or in the Free Syrian Army … none of them heard anything,” Zakarya said via Skype. “We have been trying to talk to anyone who knows anything about them. In Syria you can’t hide anything anymore. So if there is this powerful kind of group you would think we would at least hear something about it. It is very strange and awkward and it opens the door for a lot of speculation about if this group is real or not.”

There is almost no information publicly available about the Khorasan group.

The New York Times reported the group is led by Muhsin al-Fadhli, a senior al Qaeda member who was close to Osama bin Laden. Members of the organization are “said to be particularly interested in devising terror plots using concealed explosives,” the Times said.

"We did not target individual leaders," Mayville said in response to a question about whether al-Fadhli had been killed in the airstrikes. 

Andrew Tabler, a senior fellow at the Washington Institute for Near East Policy, said he thought the attacks came Tuesday morning (Monday night in the U.S.) in response to ISIS attacking Kurdish villages in northern Syria during the weekend, which prompted nearly 200,000 people to flee to Turkey.

Mayville said U.S. officials are still analyzing the effectiveness of the strikes and the attack was the “beginning of a credible and sustained campaign to destroy" ISIS. With little information about the Khorasan group, it is unclear if the U.S. and its Arab partners will continue to target it.