Four soldiers have been killed and 16 others injured during a shooting rampage at the US Army's Fort Hood base in Killeen, Texas, US.
The shooter, identified as specialist Ivan Lopez, used a .45-calibre Smith & Wesson semi automatic pistol as he opened fire on individuals in the 1st Medical Brigade area of the base, and then moved to the 49th Transportation Battalion, before dying from a self-inflicted wound.
Lopez, who had served a four-month tour of duty in Iraq in 2011, was being treated for depression, anxiety and several other psychological and psychiatric problems, including possible post-traumatic stress disorder (PTSD), at the base.
Fort Hood commander army lieutenant general Mark Milley said that the army currently does not have any evidence that links the incident to terrorism, but added they are 'not ruling anything out'.
"Our focus now is on the families of the injured, and on the families of the killed [to] ensure they have the best care and counselling available," Milley said.
Eight injured soldiers are being treated at Baylor Scott & White Health Hospital in Temple, Texas, while the remaining patients were taken to Darnall Army Medical Center, CNN reports.
Baylor Scott & White Health's chief medical officer Dr Glen Couchman said three patients were in a critical condition, while 'the remaining are all seriously injured'.
Meanwhile, US President Barack Obama said an investigation is underway to determine exactly what happened.
"We are going to do everything we can to make sure that the community at Fort Hood has what it needs to deal with the current situation, but also any potential aftermath," Obama said.
Fort Hood, which houses 45,414 assigned soldiers and 8,900 civilian employees, also witnessed a shooting attack in November 2009, which left 13 soldiers dead and more than 30 wounded.
The gunman, a former US Army major and psychiatrist, Nidal Malik Hasan, was sentenced to death for the massacre in August 2013.
Image: A file photo of Darnall Hospital at Fort Hood, Texas, where injured personnel are being treated. Photo: courtesy of Michael Heckman, III Corps PAO.