Defense Secretary Leon Panetta says the death penalty is a consideration as the military moves to investigate and possibly put on trial a U.S. soldier suspected of gunning down 16 Afghans.

In his first public remarks on the incident, Panetta said Monday the shootings must not derail the military mission in Afghanistan, and pressure to do so from political leaders in Kabul and Washington must not alter that course.

He said the U.S. seems to get confronted every other day with challenges that test U.S. leadership and its commitment to the mission.

Panetta shed little light on what may have triggered the weekend massacre, but said officials will use the military justice system, and that capital punishment is possible.

He spoke with reporters traveling with him to Kyrgyzstan on Monday.