A US army psychiatrist accused of killing 13 people in a shooting spree at a Texas base has claimed the United States is at war with Islam, a network reported Saturday.

Fox News said Nidal Hasan made the claim in an exclusive six-page statement that did not directly address the 2009 massacre.

"My complicity was on behalf of a government that openly acknowledges that it would hate for the law of Almighty Allah to be the supreme law of the land," Hasan wrote.

He then, according to Fox, apparently asked if this was a war on Islam. "You bet it is," he said. "I participated in it."

Hasan's long-awaited trial began with jury selection on July 9.

The 42-year-old could face the death penalty if convicted of carrying out the mass shooting at Fort Hood where hundreds of soldiers were preparing to deploy to Iraq and Afghanistan.

The November 2009 shooting is the worst on a military base in US history and led to an outcry for greater security from "homegrown" terror acts.

Hasan is also accused of wounding 32 fellow soldiers during the massacre -- people who may end up being cross-examined by the accused after he fired his lawyers and opted to represent himself.

Hasan wanted to use a "defense of others" strategy to justify his actions. But military judge Colonel Tara Osborn prohibited him from doing so after ruling that the argument had no merit.

In a copy of Hasan's intended opening statement, he acknowledged that "it's not going to be easy" to convince a jury made up of soldiers that his actions were justified

Hasan was born in Virginia to Palestinian parents and raised in the US state.

His court martial is expected to begin August 6.