Updated

President Obama, once again consoling a nation after a deadly shooting at a military post, joined with the families of those killed last week at Fort Hood in mourning their loss -- and vowed to do more to secure America's military facilities.

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"Their passing shakes our soul," Obama said Wednesday during a memorial service at Fort Hood.

Obama spoke in a setting that has become all too familiar for the commander-in-chief. The shooting was the second at Fort Hood since 2009, and followed last year's massacre at the Washington Navy Yard.

Military leaders spoke in disbelief that, once again, the sense of safety on post has been shattered. They once again urged the Army, the military and the country to come together.

"As we have in other difficult times, we will have strength in unity," Gen. Raymond Odierno, Army chief of staff, said. "We will all stand together as an Army."

Obama said this tragedy occurred in a place "where they're supposed to be safe." Referencing the 2009 mass shooting where 13 were killed, he said: "This tragedy tears a wound still raw from five years ago."

Three were killed, in addition to the shooter, in last week's rampage. Sixteen were wounded.

Though momentum on Capitol Hill has faded for any kind of aggressive firearms legislation, Obama urged the country to honor the victims' lives "in deed and truth," with a renewed commitment to counsel those with mental health issues and to keep guns out of the hands of those with mental health problems. And, amid criticism that U.S. military bases are falling short on security, Obama said the military should do "everything in our power to secure our facilities and spare others this pain."

Army investigators are still piecing together what led to Spc. Ivan Lopez's deadly, eight-minute rampage last week, on the same sprawling post where an Army psychiatrist unloaded on his comrades five years earlier.

Even after Fort Hood's second deadly shooting, military officials have warned that screening all soldiers for weapons as they enter the 108,000-acre base isn't feasible.

Adding complexity to the president's response are questions about whether the suspect's wartime service precipitated his actions. Although Lopez did a short stint in Iraq in 2011 and said he suffered a traumatic brain injury, Fort Hood officials have said his mental condition was not a "direct participating factor" in the shooting.

The Associated Press contributed to this report.