AFP - A former White House security adviser has alleged that the Muslim army psychiatrist accused of killing 13 at a Texas military base may not have been investigated because of "political correctness."

Frances Fragos Townsend, a Homeland Security adviser to president George W. Bush told US lawmakers she was worried that the chief suspect, Major Nidal Malik Hasan, was not properly investigated despite warnings he may have been dangerous.

Hasan has been charged in the deadly shootings in the Fort Hood army base that killed 13 and wounded 42 on November 5.

Townsend cited several red flags that could have spurred authorities to act, including a poor job evaluation, questionable statements, and Hasan's e-mail communication with a radical Yemeni cleric.

"Regrettably I worry about a sense of political correctness," she said, testifying at the Senate Committee on Homeland Security.

"I worry that in a post-9/11 world... there might have been some sort of self-censoring, if you will, a reluctance for them to pursue a senior uniformed military member, a doctor who is Muslim," said Townsend.

She added that US officials "very much respect and rely on the vast majority of law-abiding Muslims, and we've done tremendous cultural training inside the federal government and law enforcement agencies" regarding Islam.

Senator Joe Lieberman, who chairs the Senate committee, said he was investigating whether the government failed "to connect the dots in a way that enabled Hasan to carry out his deadly plan."

The US army has launched a separate investigation. Related article: Pentagon launches Fort Hood probe

Retired Army General John Keane said that while the army has clear guidelines for identifying and handling white supremacists, no such guidelines exist for people advocating radical Islam.

"It should not be an act of courage for a soldier to identify a soldier that is displaying extremist behavior," he said. "It should be an obligation."

But Juan Carlos Zarate, a former deputy national security adviser, echoed warnings from President Barack Obama not to jump to conclusions.

"The Fort Hood case could prove to be even more complicated than past events. It may be that we will not see a smoking gun that revealed Major Hasan's true motivations and signaled an intent to resort to violence."

The 'lone wolf' threat "is the most challenging and difficult of problems for the counter-terrorism and law enforcement communities," Zarate said.

"Attacks by such actors are difficult to predict and to prevent -- even more so when they are acting from the inside," he added.

Hasan had been repeatedly warned over his poor job performance as long ago as 2007, US media reported Thursday.

National Public Radio published on its website a transcript of a memo dating from May 2007 that raised "serious concerns" about Hasan's "professionalism and work ethic."

The memo is signed by Hasan's supervisor at the time, Major Scott Moran, a senior military psychiatrist at the Walter Reed Army Medical Center in Washington DC, where Hasan was being trained.

At one point Hasan "was counseled for inappropriately discussing religious topics with his assigned patients," the memo says.

He was warned for "having a poor record of attendance at didactics and lower than expected ... scores," as well as for being "consistently late" to morning reports and for being overweight.