The United States and its allies from five Arab nations launched airstrikes against Islamic State militants in Syria on Monday, expanding the war against ISIS beyond the borders of Iraq — but ISIS was not the only target.
The U.S. blasts also hit training camps, weapons production facilities and other buildings that belonged to a shadowy group known as the Khorasan.
The decision to attack the Khorasan along with ISIS reportedly came at the last minute as a result of intelligence that this al-Qaeda affiliate may have been close to completing a plan to attack the United States.
"It must be clear to anyone who would plot against America and try to do Americans harm, that we will not tolerate safe havens for terrorists who threaten our people," President Barack Obama said at the White House on Tuesday.
Below, we've answered a few basic questions about the group, which is only becoming publicly known in recent days.