Sen. Elizabeth Warren says there are "more questions than answers" about what led to four US soldiers being killed in the October 4 Niger ambush, and she's arguing for Congress to have a bigger role in determining how US troops operate in countries like Niger where they don't have an active combat mission.

Warren, who sits on the Senate armed services committee, told CNN the attack was yet another sign that Congress is long overdue to debate a war authorization that better defines the US' counterterrorism role.