US President Barack Obama has paid tribute to the victims of last week's shooting spree at Fort Hood's military base in Texas and vowed justice for the 'craven' act.

In a sometimes emotional memorial ceremony, Obama stressed that the fact that the deadly incident happened in US soil has made it even more painful.

US Army psychiatrist Major Nidal Hasan opened fire on fellow soldiers at the Texas base on Thursday, killing 13 troops and wounding 42 others.

Hasan was shot by the police four times. He is now recovering at a military hospital in Texas and has talked to his lawyer.

"These Americans didn't die in a foreign field of battle. They were killed here on American soil…this is the fact that makes this tragedy even more painful, even more incomprehensible," Obama told a large crowd of mourners.

He also warned that 'no faith justifies these murderous and craven acts', adding, “The killer will be met with justice, in this world and the next".

Defense and law enforcement officials said Hasan would soon be charged in a military court for murder.

On Tuesday, the Senate Homeland Security Committee announced it would hold a full investigation into the attacks starting with a public hearing next week.

Even as Obama honored the dead, there was government finger-pointing over the FBI's revelation that the 39-year-old army psychiatrist had been scrutinized in 2008 for contacts with an al-Qaeda-linked radical cleric, but was released without further investigation.

They claimed that it was 'decided' at the time that the case did not merit further inquiry.

The revelation provides fresh evidence that the military had been keeping an eye on Hasan before the shooting rampage.

Thursday's attack comes at a trying time for the US as it struggles through the deadly wars in Iraq and Afghanistan.

Only two weeks ago, Obama honored the remains of 18 soldiers killed in Afghanistan at Dover Air Force Base in Delaware.

FF/AKM