ABOARD A US MILITARY AIRCRAFT: The US soldier suspected of killing 16 Afghan civilians in a shooting rampage could face the death penalty if convicted, US Defense Secretary Leon Panetta said Monday.

The Pentagon chief told reporters aboard his plane en route to Kyrgyzstan that the suspect in the Afghan shooting spree would be brought to justice under the US military legal code, which allows for the death penalty in some cases.

Asked if the suspect could be sentenced to death, Panetta said: "My understanding is in these instances that could be a consideration."

Panetta condemned the incident as a "terrible loss of life" and said it remained unclear what may have led the gunman to murder civilians.

After walking off his base, the suspect entered Afghan homes and fired on civilian families, "then at some point after that came back to the forward operating base and basically turned himself in. Told individuals what happened," Panetta said.

When asked if that amounted to a confession, Panetta said: "I suspect that was the case."

"We're not sure, what the reasons were. But he is in custody. I have assured President (Hamid) Karzai that he will be brought to justice and held accountable," the US defense chief said.

Panetta repeated the US administration's stance that the shooting, the latest in a spate of damaging incidents that have strained US-Afghan relations, would not derail the war effort or force a change to the current strategy, which calls for a gradual drawdown of US and NATO troops through 2014.

"We cannot allow these events to undermine our strategy or the mission that we're involved in," Panetta said. "It's important that we push on," he said.

The US soldier walked off his base in southern Kandahar province and broke into three village homes before dawn Sunday, killing 16 people including women and children -- an event described by Karzai as "unforgivable." AGENCIES