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."

Despite demands from the Afghan parliament for a public trial, Panetta's remarks echoed earlier statements from Washington that the rogue soldier would be tried in a US military court.

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."

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

"We're not sure why, what the reasons were," he said.

"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 force a change to the current strategy, which calls for a gradual drawdown of US and NATO troops through 2014.

The shooting spree followed violent unrest last month that erupted after US soldiers burned Korans at the Bagram airbase, with 40 people killed in the rioting.

President Barack Obama and top commanders apologized for that incident, which they said was an accident and not intentional, but the episode has plunged US relations with Kabul into a serious crisis.

"War is hell. These kinds of events and incidents are going to take place," Panetta said of the shooting.

But he portrayed the attack as an isolated incident and said "we cannot allow these events to undermine our strategy or the mission that we're involved in."

"It's important that we push on, and that we bring this war to a responsible end and achieve the mission that all of us are embarked on," he said.

The Pentagon chief insisted that the war effort was not in jeopardy, and that the Afghan government continued to cooperate while Afghan army and police remained steadfast partners.

As evidence, he cited how Afghan forces have responded to protests over the Koran burning and the shooting attack in Kandahar province.

"The Afghan army is doing very well in maintaining order. We're not getting large-scale desertions, we're not getting any kind of disruptions. They recognize what they have to do and they're doing it," he said.

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

Panetta said he was headed to Bishkek to speak to Kyrgyz leaders about the "importance" of the Manas air base outside the city, a vital hub used to ferry troops to the war in Afghanistan and refuel warplanes.

"I want to thank them and ensure that relationship can continue into the future as well," he said.

After Kyrgyzstan threatened to cancel US access to the base in 2009, Washington agreed to pay Bishkek $60 million a year for use of the air field, up from an earlier annual fee of about $17 million, officials said.

The current deal is due to expire in the summer of 2014.