The government says the killing of al-Awlaki has raised the risk of anti-American violence, and they fear that supporters of the cleric will seek to avenge his death.
ABC News has learned that the FBI is warning police around the country that the killing of al-Awlaki could provoke revenge attacks in the U.S. The American-born radical was taken out Friday by a U.S. force of drones and support aircraft that fired three hellfire missiles killing what U.S. officials call "the most dangerous man on the planet."
"He can no longer threaten America, our allies or peace loving people around the world," said Secretary of State Hillary Rodham Clinton.
"This country is much safer as a result of the loss of Awlaki," said Secretary of Defense Leon Panetta.
In the new travel bulletin, the Department of Homeland Security warned that al Qaeda in Yemen could soon "attempt to retaliate directly against the homeland for Awlaki's death."
"Due to Awlaki's popularity online, we are concerned about the possibitliy that autonomous extremists may react violently," the bulletin adds.
This means that al-Awlaki could be seen as a martyr, inspiring some loner, unknown admirer to attack out of revenge.
A second American-born terrorist perished in the attack - Samir Kahn, who edited al-Awlaki's online magazine which targeted the U.S. There may also have been another important victim, too
U.S. officials said they believed al Qaeda's top bomb maker, Ibrahim Hassan al-Asiri, was killed in the attack. A top Yemeni official said that was not the case.
Al-Asiri is described as the "evil genius" of al Qaeda, responsible for plotting and devising ways around airline security.