U.S. federal investigators are probing what they say is an act of domestic terrorism, after a bomb was found along a parade marking the holiday for slain civil rights leader Martin Luther King, Jr.
A backpack containing the explosive device was found Monday in the city of Spokane, in the northwestern state of Washington.
The head of the FBI office in the region, Frank Harrill, said the bomb was potentially deadly, and called the incident an act of domestic terrorism that was meant to advance a political or social agenda.
Harrill said agents have not yet determined a motive, but recognize that it could be linked to the federal holiday honoring King, an African-American who was assassinated in 1968.
A number of racist groups operate in and around the Spokane area, including the white supremacist Aryan Nations.