An official investigation suggests Maj. Nidal Hasan was promoted despite documented complaints about his strident religious views and unprofessional behaviour. (Uniformed Services University of the Health Sciences/Associated Press)

A U.S. Senate committee urged the Defence Department to take firmer steps to combat what it sees as the threat of "Islamist extremism" within the military's ranks, calling the current procedures inadequate for heading off possible attacks like the shootings at Fort Hood, Texas.

The recommendations by leaders of the homeland security and governmental affairs committee come as the Pentagon is preparing to release an internal review of the Nov. 5 Fort Hood massacre that left 13 people dead.

The review will propose ways to improve the American military's ability to identify service members who may be a danger to others and quicken reaction times by emergency response teams.

Led by Senator Joe Lieberman, the committee's investigation of the Fort Hood has focused on whether the military missed numerous signs the accused shooter, Army psychiatrist Maj. Nidal Hasan, had embraced a radical view of Islam.

In a Jan. 13 letter to Defence Secretary Robert Gates, Lieberman, along with Senator Susan Collins, contend the threat of "homegrown terrorism" inspired by violent Islamic extremism is growing and the military isn't exempt.

As a result, the Defence Department's existing policies for dealing with personnel that become involved in gangs and racist groups need to be expanded to cover new avenues of violence, Lieberman and Collins say.

Not only will that head off future attacks, it will protect Muslim-Americans in the military from suspicion, they said.

"Efforts by [the Defence Department is] to educate its personnel concerning what violent Islamist extremism is and what the warning signs of such extremism are — as distinguished from the practice of the Islamic faith — will increase trust between the thousands of Muslim-Americans serving honourably and their colleagues," they wrote.

Lieberman and Collins say their investigation of the Fort Hood shooting is still under way and they will likely make further recommendations.

Lt.-Col. Jonathan Withington, a Pentagon spokesman, said the recommendations are "precisely the type of issues" that the Defence Department's review related to Fort Hood was charged with examining.

That review includes "identifying and addressing possible gaps and/or deficiencies in the [Defence Department's] programs, processes, and procedures related to identifying department employees who could potentially pose credible threats to themselves or others," he said.