Fort Hood
Ivan Lopez is believed to be the Fort Hood shooter. Reuters/III Corps Public Affairs/U.S. Army/Handout

Update 12:15 p.m. EDT: The Fort Hood shooter has been identified as Spc. Ivan Lopez, a man who worked in the base's transportation segment. As it turns out, one of the buildings he opened fire in housed Fort Hood's transportation administration. The suspect also opened fire in another building, and drove in his car between the two. The shooter was engaged by a female military police officer in a parking lot before he fatally shot himself in the head, said the Army post's commander, Lt. Gen. Mark A. Milley, CNN reported.

The suspect, a soldier who had served in Iraq, "had behavioral health and mental health" issues, Milley told reporters late Wednesday. There was no known motive for the shooting, the general said.

"There is no indication that this incident is related to terrorism, although we are not ruling anything out," Milley said at a news conference. The initial report is the incident started as a soldier-on-soldier attack, law enforcement sources told CNN.

Milley spoke about the man who killed three people and wounded 16 others, some critically. The suspect was married and had family at the base. He transferred to Fort Hood in February and was receiving treatment and being medicated for mental health issues.

The specialist suffered from depression, anxiety and other psychiatric complaints and was going through the process that's required to diagnose Post-Traumatic Stress Syndrome, according to CNN. "He was not diagnosed, as of today, with PTSD," Milley told reporters. That process takes time.

Update 11 p.m. EDT: Speaking at a news conference, Lt. Gen. Mark A. Milley, the Army base's commanding general, told reporters that the gunman died of a self-inflicted gunshot wound. The general said that the shooter used a weapon that was purchased recently and that was not registered on the base. During his attack, the shooter engaged another member of the military before turning the gun on himself. The shooter served in Iraq in 2011, Milley said.

Update 9:45 p.m. EDT: On a conference call with journalists, Rep. Michael McCaul (R-Texas), who is chairman of the Committee on Homeland Security, said authorities had identified the Fort Hood shooting suspect as Ivan Lopez, but that a motive for the shooting remained unclear, the New York Times reported. The shooter was wearing an Army uniform, but it was unclear whether he was on active duty, McCaul said. U.S. officials do not believe terrorism was a factor in the shooting on Wednesday. The gunman, who reportedly used a 45-caliber Smith & Wesson semi-automatic handgun and wore combat fatigues, killed four people, including himself.

Update 9:15 p.m. EDT: The shooting incident at Fort Hood, which is still on lockdown,brings back awful memories of the Nov. 5, 2009, massacre at the Texas base, CNN pointed out.That day, Army Maj. Nidal Malik Hasan opened fire, killing 13 people and injuring 32. Hasan shot fellow soldiers at the processing center. Prosecutors maintained that the American-born Muslim went through a drastic radicalization that led to the shooting incident.

Hasan allegedly chose that November date because it was the day on which the units he was scheduled to deploy with to Afghanistan were scheduled to head through the processing center, according to CNN's website. The former Army psychiatrist was convicted of premeditated murder, and a military jury recommended he be put to death.

Wednesday's shooting incident was another horrible jolt to Fort Hood and it's central Texas community. In a statement, U.S. Sen. John Cornyn said: "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. No community should have to go through this horrific violence once, let alone twice."

Update 8:40 p.m. EDT: Multiple fatalities and multiple injuries have been confirmed as a result of the Fort Hood shooting incident, according to law enforcement and military officials. Security sweeps are being conducted at the scene, which is still considered "active," CNN reported.

Update 8:30 p.m. EDT: In a statement, President Obama said: "The situation is fluid right now...They [federal agencies] are working with folks on the ground, making sure everybody is secure...We're going to get to the bottom of exactly what happened."

Update 8:05 p.m. EDT: CNN said the total number of dead at Fort Hood, America's largest military base, is reportedly four people, including a shooter. Terrorism has been ruled out, and the incident is being called "a soldier on soldier" attack, the news site added. In a statement, President Obama said he is "heartbroken" over the incident.

Update 7:15 p.m. EDT: A gunman in the Fort Hood shooting incident has been killed, CNN reported. It isn't known whether the shooter was killed by a first reponder or if the attacker commited suicide. The attacker's name and background aren't yet known. The total number of wounded isn't confirmed, but CNN reported that between three and 15 people have been injured.

It's still unknown whether multiple shooters were involved in the attack at Fort Hood.

Fort Hood, one of the largest military bases in the world, is still on lockdown.

Original story:

There is an active shooter at Fort Hood Army base area in central Texas, according to CNN. Police said that an unknown number of people have been injured, Reuters reported, adding that the base has issued a shelter in place order for all personnel.

On Wednesday evening, sirens were going off at the base, said a CNN source. Defense Secretary Chuck Hagel has been notified of the shooting, according to CNN.

A base spokesman noted that an "incident" was under way but didn't provide other details, the news site reported.

A local sheriff's office said that it had heard there was a shooting. "They got some kind of shooting incident going on. They haven't told us anything. It was on post and being handled by the military. Fort Hood has not asked for any assistance," said Lt. Donnie Adams with the Bell County Sheriff's Office.

Fort Hood's official Twitter feed asked that all personnel on post find shelter.

Police in Waco, Texas, advised those on post to stay away from windows and to keep doors closed and locked.

"Injuries are being reported. Be AWARE!! If you are in the Ft. Hood Post area there is an on-going active shooter," the department tweeted.

All evening and night classes for the Central and Fort Hood campuses of Central Texas College (CTC) were canceled, according to the school's website. Personnel and students were told to evacuate CTC Central Campus.

Fort Hood was the scene of a shooting rampage in 2009 where a former Army psychiatrist killed 13 people and wounded 32 others.

This is a developing story.