Created: Wed, 02 Apr 2014 07:28:00 EST
Updated: Thu, 03 Apr 2014 05:53:04 EST
(CNN) -- [Breaking news alert published at 10:57 p.m. ET]
-- Four people have died -- including the suspected shooter -- as a result of Wednesday's shooting at Fort Hood, said the Army post's commander, Lt. Gen. Mark A. Milley. He said 16 people were wounded at the installation in central Texas.
-- There is no known motive. "There is no indication that this incident is related to terrorism although we are not ruling anything out," Milley said.
-- The suspected shooter "had behavioral health and mental health" issues, according to Milley.
-- An Army soldier "fired shots at individuals within the unit areas here" at Fort Hood and "the post immediately went into lockdown," Milley said.
-- The suspect was engaged by military police before he fatally shot himself in the head.
[Original story published at 10:35 p.m. ET]
Multiple people died and others were injured Wednesday when a shooter opened fire at Fort Hood, the sprawling Army post in Texas still on edge after a mass shooting left 13 dead in 2009, officials said.
A senior military official and law enforcement official said the suspected shooter was among the dead. The Army post said the report was "unconfirmed."
The initial report is the incident started as a soldier-on-soldier attack, law enforcement sources told CNN. The preliminary assessment is that the incident is not terror-related, the sources said.
Fort Hood did not give specific numbers on casualties.
Four patients were being treated at Scott & White Hospital in Temple and two others will require surgery soon after being airlifted there. The patients' conditions range from "stable to quite critical," according to a hospital official.
Others were taken to Darnall Army Medical Center, not far from the Medical Brigade building where the shooting occurred, said a soldier who lives nearby and who spoke on the condition of anonymity.
The suspected shooter was wearing combat fatigues, according to a U.S. official briefed on the shooting. The suspect is believed to have used a semi-automatic handgun, officials told CNN.
President Barack Obama was briefed and said Wednesday evening "we're heartbroken something like this might have happened again."
He was referring to the November 2009 massacre.
"I want to just assure all of us we are going to get to the bottom of exactly what happened," the President said.
Defense Secretary Chuck Hagel also was monitoring the situation. He described what happened as a "terrible tragedy."
"We know there are casualties -- both people killed and injured. We don't have all the facts yet," Hagel told reporters in Honolulu.
Sheriff's deputies from Bell County and state troopers were assisting by securing the area around the post, according to Bell County Sheriff's Lt. Donnie Adams. Authorities in the town of Killeen, just outside the gates, were also standing by to help.
"We are very concerned. Fort Hood is always there for us and we want to be there for them," said Killeen Mayor Dan Corbin.
He continued: "They are used to dealing with combat situations, and I'm sure they are very capable of handling this."
Fort Hood's official Twitter feed asked that all personnel on post shelter in place. Sirens blared.
The lockdown at the Army installation was lifted just prior to 9 p.m. (10 p.m. ET), military personnel at the front gate told CNN.
On November 5, 2009, Army Maj. Nidal Malik Hasan opened fire at Fort Hood, killing 13 people and injuring 32.
He shot fellow soldiers at the processing center. Prosecutors maintained that the American-born Muslim underwent a progressive radicalization that led to the massacre.
Hasan allegedly picked that day because it was when the units he was scheduled to deploy with to Afghanistan were scheduled to go through the processing center.
The former Army psychiatrist was convicted of premeditated murder, and a military jury recommended that Hasan be put to death.
Wednesday's shooting reminded many in the central Texas community of that incident.
"Today, Ft. Hood was once again stricken by tragedy. As Texans, our first priority must be caring for the victims and their families. Ft. Hood has proven its resilience before, and will again. Texas will support those efforts in any way we can, with any resources necessary," said Gov. Rick Perry.
U.S. Sen. John Cornyn said in a statement that no community should have to experience such violence once, let alone twice.
"Tonight, Texans' hearts are once again very heavy. The scenes coming from Fort Hood today are sadly too familiar and still too fresh in our memories," he said.
According to the Fort Hood website, the post is one of the largest in the world with 45,414 assigned soldiers and 8,900 civilian employees.
The installation, which encompasses 214,000 acres, is home to two divisions -- the Army's 1st Calvary and the 4th Infantry (Mechanized). There are 12 other units attached or based there.
CNN's Steve Almasy, Nicole Dow, Greg Botelho, Evan Perez, Shimon Prokupecz, Pamela Brown, Brian Todd, Matt Smith, Barbara Starr, Carma Hassan and Devon Sayers contributed to this report.