The US Army psychiatrist charged with killing 13 people in a shooting spree on a Texas army base has been ruled sane and thus fit for trial, a source familiar with the case said.

The ruling by a group of medical experts, called a sanity board, opens the door for a court martial that could end in the execution of Major Nidal Hasan, who was paralyzed from the neck down during the November 5, 2009 massacre.

Neither prosecutors nor retired Army Colonel John Galligan, a veteran military lawyer representing Hasan, 40, would confirm the board's decision.

But Galligan suggested it went against his client, who worked at Fort Hood until the shooting.

"I'm not going to say what they ruled," he told AFP. "I would just say this: I don't think the report will be anything that will be an impediment to the charges from the government's perspective."

Hasan is charged with killing 13 people and wounding 32 others in a crowded Fort Hood deployment center.

Witnesses at an evidentiary hearing last year fingered Hasan as a ruthless murderer who cried out "Allahu akbar!" before gunning down troops and civilians alike.

The army has come under fire for missing numerous warning signs about Hasan, who had been in email communication with Anwar al-Awlaqi, a radical US-born cleric now being hunted in Yemen as an Al-Qaeda associate.

The army has not said if prosecutors would seek the death penalty.

But the military judge who oversaw the evidentiary hearing told commanders that he believed it should be a capital case after determining there was sufficient evidence for trial.

The next move, though, is on hold. An army officer charged with deciding how the case proceeds has agreed to delay any action until February 23.

Even if a trial is ordered, it probably won't take place for at least a year, said Colorado-based military attorney Frank Spinner.

The sanity board consists of one or more experts who are physicians or clinical psychologists.

Sanity is determined by deciding if a defendant "understands and appreciates" the criminality of his actions, said retired army Colonel Calvin Lewis, who teaches at the Texas Tech School of Law in Lubbock.

Galligan wouldn't divulge details of the board's decision or say how his client reacted when they met at a jail in Belton, 20 minutes east of Fort Hood.

But he called the board's report, filed last Friday, a creation of the prosecution that was "issued without having the benefit of all the evidence out there."

Fort Hood spokesman Chris Haug said the sanity board report went to Colonel Morgan Lamb, a brigade commander on Fort Hood.

He is expected to hand off the decision on calling a trial to post commander Lieutenant General Robert Cone, who is currently serving in Iraq, because only a general can order a capital murder proceeding.

The issue of Hasan's mental state at the time of the shootings may not be over, cautioned military attorney Geoffrey Corn, a professor at South Texas College of Law in Houston.

The defense, he and other attorneys agreed, can dispute the sanity board report once a trial has been ordered.

"The judge could order a hearing in the court," explained Corn, a retired Army officer and law-of-war expert.

"The judge could have the psychiatrist come and testify in a motion to determine the defendant's competence to stand trial."