Defense Secretary Jim Mattis and Secretary of State Rex Tillerson will testify before the Senate Foreign Relations Committee Monday evening about the possibility of a new congressional war authorization following a deadly ambush on U.S. troops in Niger.

The 5 p.m. open hearing with top administration officials about replacing 9/11-era legislation with a new authorization for the use of military force, or AUMF, allowing the Trump administration to fight terrorist groups, comes as questions swirl over how an Islamic State-affiliated group surprised U.S. military advisers in West Africa and killed four soldiers.