The Obama administration says the killing of a U.S.-born cleric in Yemen has raised the risk of anti-American violence worldwide.
The State Department says the death of Anwar al-Awlaki would provide motivation for individuals or groups to retaliate against U.S. citizens or American interests.
A department warning issued Saturday notes that al-Awlaki and other members of Al-Qaida in the Arabian Peninsula previously called for attacks against the U.S., and the warning says his supporters could seek to avenge his death.
Al-Awlaki was killed during an attack on his convoy early Friday.
The State Department issued a similar alert after Osama bin Laden was killed in Pakistan. This latest alert is set to expire at the end of November.