A shooting took place at the US military base at Fort Hood in Killeen, Texas on Wednesday afternoon. Four people were confirmed dead including the gunman, apparently of a self-inflicted wound.

Sources told CBS News that the shooter was a 34-year-old soldier named Ivan Lopez. While little is known about Spc. Lopez, sources told CBS the Wednesday shooting may have been motivated by a conflict with another soldier.

Lt. Gen. Mark A. Milley confirmed during a Wednesday evening press conference that there was only a single male shooter, but refused to divulge the gunman’s name as the family has yet to be notified. Milley said the soldier in question was receiving treatment for depression and anxiety, and was undergoing the process that would have ultimately determined if he had post-traumatic stress disorder (PTSD).

The Fort Hood gunman was found wearing combat fatigues and used a semi-automatic handgun.

The suspect served a four-month tour of duty in Iraq in 2011 and may have suffered a traumatic head injury during his time overseas, Milley said. The soldier only arrived at Fort Hood in February and has a wife and family in the Killeen area.

“Our focus now is to focus on the families of the injured and the families of those killed,” the general said. He encouraged the public to turn over any information that might be relevant to an investigation to either the FBI, local police, or military investigators.

As many as sixteen people have reportedly been hospitalized. Three of the wounded have suffered critical injuries and were transported to Carl R. Darnall Medical Center and other area hospitals.

All personnel on post are asked to shelter in place. The gunman was believed to be inside the Medical Support Building, the suspect could be barricaded inside that area. — Fort Hood (@forthood) April 2, 2014

Witnesses speculated that 20 shots were fired from a .45 pistol.

One soldier told KENS-5 in Texas that the first gunshots rang out around 4:35 p.m. near the outdoor motor pool but the gunman then ran into the medical building. The witness said it seemed like some kind of standoff had taken place, and that some people tried to flee by jumping over a seven-foot-high barbed wire fence.

Fort Hood soldiers watching the news from Fort Irwin. pic.twitter.com/YYE9mv4oUn — Don Gomez (@dongomezjr) April 2, 2014

An estimated 90 police and military vehicles were at the scene two hours after the first shots, along with nearly two dozen ambulances and SWAT teams.

There were also reports of victims in the Battle Simulation Center on 65th and Warehouse.

The lockdown was lifted Wednesday night, allowing many families to reunite with loved ones who were either stuck in traffic on the way to the base or were waiting for loved ones to arrive there. The American Red Cross previously announced that it had opened a shelter with a capacity of 150 for families who may have had trouble returning to Fort Hood amid the confusion.

The parking lot outside the base, where thousands of people come and go on a daily basis, quickly filled with family members of military personnel anxious for news on the situation. Local media reported that, along with fear and concern, a number of people were voicing frustration that another shooting appears to have taken place after Nidal Hasan, a US Army major and psychiatrist, fatally shot 13 people and injured more than 30 others on the base in 2009.

Hospital officials said Wednesday night that the victims had been shot in the head, chest, neck, abdomen, and extremities. They added that, in the wake of the 2009 shooting, hospital staff carried out drills to prepare for a mass shooting incident.

“Their conditions range from stable to quite critical,” one doctor said in an evening press conference. “There’s a lot of unknowns early on and it creates some logistical problems...I’m pleased to report we were well prepared but it always takes a little while to figure out how many patients are going to come.”

Officials have not confirmed whether Lopez was in uniform at the time of the shooting, which was reportedly motivated by an argument at the Army base's motor pool. It is known that he was living in the Killeen area. Terrorism is not suspected as a motivating factor.

Texas Governor Rick Perry, who was also governor in 2009, released a statement expressing condolences to the families of the victims.

“Today, Ft. Hood was once again stricken by tragedy,” he said. “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. The thoughts and prayers of all Texans are with everyone affected by this tragedy.”

Speaking to a press pool in Chicago on Wednesday afternoon, US President Obama said he is “heartbroken” about the events at Fort Hood and promised “we will get to the bottom of what happened.”

"It's a terrible tragedy. We know that. We know there are casualties, both people killed and injured," Defense Secretary Chuck Hagel told reporters during a news conference in Honolulu.

"We don't have all the facts yet. We will get those. It's still under investigation," he added.

The FBI had launched a manhunt for a former military recruit who told friends he was planning a “jihad” attack on Fort Hood, according to a Fox News report published Tuesday night. The FBI confirmed the report, although officials said the suspect had been interviewed and that he was not considered a threat.