The United States is doing what it must to "take the fight to terrorists," leading a coalition of Arab nations in a series of airstrikes against the so-called Islamic State terror group in Syria, U.S. President Barack Obama said Tuesday.
At the same time, the United States took action - on its own - against another terrorist organization, the Khorasan Group. Obama described its members as "seasoned al Qaeda operatives in Syria."
U.S. officials said the group was plotting attacks against the United States and other Western targets.
The plots against the United States were discovered by the intelligence community in the past week, an intelligence source with knowledge of the matter told CNN. The source did not say what the target may have been, but said the plot potentially involved a bomb made of a nonmetallic device like a toothpaste container or clothes dipped in explosive material.
A plot involving concealed bombs on airplanes "was just one option they were looking at," a U.S. official said.
"Once again, 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," Obama said in televised remarks from the White House.
Concern over a possible backlash by the terror groups has prompted the U.S. Department of Homeland Security to issue a bulletin warning law enforcement agencies to be on heightened alert for lone-wolf terror attacks on U.S. soil in wake of the airstrikes, a U.S. law enforcement official with knowledge of the warning told CNN.
The bulletin calls for vigilance as well as scrutinizing social media for anyone encouraging violence in response to the strikes, according to a U.S. law enforcement official with knowledge of the warning's contents. It points to the use of social media as a tactic by ISIS to spread its message and call for violence.
It also advises agencies to look for changes in appearance or behavior in those they're tracking, the official said.
See more on this developing story on CNN.com