The Department of State warned U.S. citizens worldwide about possible retaliation attacks after the death of a radical U.S.-born cleric in Yemen earlier this week.
Anwar al-Awlaki, along with several other militants, was killed early on Friday in eastern Yemen in what Yemeni newspapers say was a suspected CIA drone strike.
"The death of Awlaki, in the near term, could provide motivation for anti-American attacks worldwide from individuals or groups seeking to retaliate against U.S. citizens or interests because of this action," the U.S. Department of State said.
"Awlaki's standing as a preeminent English-language advocate of violence could potentially trigger anti-American acts worldwide to avenge his death," the department's travel alert reads.
The warning will remain in place until November 30.
The FBI and the Department of Homeland Security also warn about possible retaliation from extremists on the U.S territory.
"We assess the death of [Awlaki], in the near term, could provide motivation for Homeland attacks - particularly from HVEs [homegrown violent extremists] seeking retaliation," ABC News quoted an intelligence bulletin as saying.