A US soldier who fled his post as a Muslim conscientious objector was convicted Thursday of plotting an attack on a Texas military base, prosecutors said.

Naser Jason Abdo, 22, faces a maximum sentence of life in prison over the plot to attack soldiers and their families at the Fort Hood base in Texas, the scene of a deadly shooting rampage in 2009.

He was arrested after a store clerk became alarmed by Abdo's demeanor while he paid $256.44 in cash for a number of items including smokeless gunpowder.

"It's important to note that this plot was interrupted and a potential tragedy prevented because an alert citizen notified law enforcement of suspicious activity, triggering prompt investigation and intervention," said Robert Pitman, US attorney for the Western District of Texas.

Police found a handgun, enough gunpowder to make at least one bomb and directions from an Al-Qaeda magazine on how to build an explosive device when they searched Abdo's discount hotel room near the base.

Witnesses also testified that Abdo had intended to kidnap a soldier and execute him on video.

But the plan fell apart and Abdo fled, leaving his Cadillac, body bags, a green body bag carrier and bleach to clean up the crime scene. He had also acquired a stun gun and a cattle prong.

One witness testified at trial that Abdo told him that the assault was intended to show support for Army Major Nidal Malik Hasan, a Muslim psychiatrist accused of killing 12 soldiers and a civilian in the 2009 shooting, which also wounded 32 others.

The FBI alleges Hasan had contacts with radical US-born cleric Anwar al-Awlaqi, a leading member of Al-Qaeda in the Arabian Peninsula who was killed in a September 2011 drone strike.