UPDATE

A soldier has killed three people and wounded 16 before turning the gun on himself at Fort Hood, the US military base devastated by a deadly 2009 rampage, the commanding general says.

Lieutenant General Mark Milley said on Wednesday the gunman, who served in Iraq in 2011, was being treated for depression and anxiety, and being checked for possible Post-Traumatic Stress Disorder (PTSD).

All of the dead and wounded were military personnel.

“At this time, there is no indication that this incident is related to terrorism, although we are not ruling anything out,” Milley told reporters at the sprawling US army installation in Texas.

“We do not know a motive. We do know that this soldier had… mental health issues, and was being treated for that.”

The gunman – who was not immediately identified pending notification of next of kin – used a .45-calibre semi-automatic pistol, which he bought recently and apparently smuggled onto the base.

He opened fire in a medical building, got into a vehicle while still shooting and then went to another building.

The assailant killed himself when he was engaged in a parking lot by an armed female military policewoman, shooting himself in the head, said Milley.

The general praised the servicewoman’s courage, saying it was “clearly heroic.”

Milley said the Fort Hood gunman was “currently under diagnosis for PTSD but had not been diagnosed with PTSD.” The shooter, who was married, was on medication and had reportedly told officials that he had suffered a traumatic brain injury.

CBS News and other media, citing unnamed sources, identified the shooter as a 34-year-old Army specialist.

The US army base remained on lockdown for a couple of hours after staff were ordered to shelter in place, but personnel and family members were later given the all-clear.

A soldier told CNN he heard gunshots “and assumed they were blank rounds… We then heard a burst, another burst and it was clear they weren’t blank rounds. They were live rounds.”

The incident sparked memories of the November 2009 shooting at Fort Hood, when Major Nidal Hasan opened fire at the base, killing 13 people and wounding more than 30 others.

Hasan, who was shot during the attack and is partially paralysed, was sentenced last year to death. The US-born Muslim of Palestinian descent is awaiting execution.

President Barack Obama said he was “heartbroken something like this might have happened again,” and pledged that investigators would “get to the bottom of what happened.”

“Obviously, this reopened the pain of what happened at Fort Hood five years ago,” Obama said.

“Many of the people there have been on multiple tours in Iraq and Afghanistan. They serve with valour, they serve with distinction. At when they’re at their home base, they need to feel safe.”

Fort Hood is spread out over almost 900 square kilometres, and is the largest US military base with a population of 70,000 including 42,000 military personnel. The rest are family and civilian staff.

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