Death toll of the shooting spree at the U.S. Army base at Fort Hood may rise from the current 13 as some of the hospitalized victims have "extremely serious injuries" and several of them are still at "significant risk" of losing their lives," a doctor said Saturday.

Tears stream down US Army Sgt Major Leroy Walker Jr.'s face during a candle light vigil at Hood Stadium on the Fort Hood Army Post in Fort Hood, Texas November 6, 2009. The death toll from an Army psychiatrist who opened fire at the Fort Hood Army post rose to 13 on Friday, and Army officials said the suspected shooter was hospitalized and on a ventilator.[Xinhua/Reuters Photo]

Of the six who were in the ICU on Thursday when the shooting spree occurred, only two are left.

"The two patients who remain in the ICU are no longer on ventilators and have been quite stable," he said. "So a lot of progress has been made."

But Smythe admitted that some of the patients may be physically impaired for the rest of their lives, and that "there is certainly no doubt that many of them will be psychologically impaired for the rest of their lives."

Thirty nine-year-old Army psychiatrist Nidal Malik Hasan was accused of opening fire at Fort Hood Thursday in an attack that left 13 dead and 30 others wounded. Hasan, who was shot multiple times, was in stable condition and taken into custody.

Media reports said Hasan, a U.S. citizen of Jordanian descent, was going to be dispatched to Iraq or Afghanistan and he "was disturbed" about his overseas deployment.