The Pentagon has responded to the massacre at an army base in Texas by deciding to screen all United States defence services for staff who are unstable and potentially violent.

News of the urgent review broke as the Pentagon revealed that soldier suicides this year would set another record.

Last week, 13 people were killed at Fort Hood in Texas when an army psychiatrist allegedly opened fire.

Now the military has to satisfy itself that there are not other potentially dangerous service members who could repeat the gruesome massacre at Fort Hood somewhere else.

And more broadly, the Pentagon is examining how all the military services keep a watch on potential problems in their ranks.

The Army Chief of Staff, General George Casey, had announced his own internal investigation.

There were reports it would start with the Walter Reed military hospital, where alleged Fort Hood gunman army Major Nidal Hassan spent six years.

It would investigate how the military missed signs of Major Hassan's instability and potential violence.

But that investigation now looks as though it will include all defence services.

The massacre was to have been the subject of the Senate Homeland Security committee hearing on Thursday but the White House has refused to provide any government officials as witnesses.

The White House has also taken control of the congressional briefings on the massacre, with committee chairs all told briefings would be handled by the president's national Security Council due to the sensitive and high-profile nature of the case.

Mental illness, suicide

That case has also thrown a light on mental illness within the US military.

Today General Peter Chiarelli - the army vice chief of staff - released figures showing for the fifth year in a row suicides in the US army would set a new record.

"As of 16th November, the army has reported 140 active duty suicides, which is equivalent to our total in 2008 with a month and a half remaining in the year," he said.

Those statistics do not reveal the whole picture because they do not include figures on people after they have left the military.

A congressional research service report last year found that the real incidence of suicide among veterans simply is not known.

But based on figures from the Centres for Disease Control and Prevention, Veterans Affairs estimated that 18 veterans a day - or 6,500 a year - take their lives.

General Chiarelli says the cause of the rising suicide rate among active service members is unknown.

About one-third of the suicides are among soldiers who have not been deployed to a combat zone.

"Over the past eight months, every suicide has been briefed to me," General Chiarelli said.

"And although we have made changes to army policy based on many of the lessons learned, we still haven't found any statistically significant causal linkage that would allow us to effectively predict human behaviour.

"The reality is, there is no simple answer. Each suicide case is as unique as the individuals themselves."

Preventing suicides

At the beginning of last month, the US army began what it called a comprehensive soldier fitness program.

In an era where US troops take multiple tours of duty with minimal breaks at home, Brigadier General Rhonda Cornum said there needed to be a greater emphasis on mental wellbeing.

"We have spent a lot of time historically on training physical fitness and technical excellence in the army, but not psychological fitness," she said.

"And all three are really essential in this era of persistent conflict."

Basic training now includes anti-stress programs as part of a broader effort to help soldiers deal with the after-effects of combat and prevent suicides.