President Barack Obama said Friday the entire nation is grieving for those slain at Fort Hood, and he urged people not to jump to conclusions while law enforcement officers investigate the shootings.

Obama met Friday morning with FBI Director Robert Mueller and other federal leaders to get an update on what they've learned. Thirteen people were killed and 30 others injured in the shooting rampage at the Texas Army post on Thursday. The suspected shooter is an Army psychiatrist; his motive remains unclear.

"We don't know all the answers yet. And I would caution against jumping to conclusions until we have all the facts," Obama said in a Rose Garden statement otherwise devoted to the economy.

"What we do know is that there are families, friends and an entire nation grieving right now for the valiant men and women who came under attack yesterday," the president said.

His aides, meanwhile, worked to make way for Obama to attend a still unscheduled memorial service for those slain at the nation's largest military post. The White House's top spokesman said Obama would attend that service and emphasized it would take place at the family's convenience, and that it will not be dictated by the president's schedule.

"When a service is scheduled, the president will attend," Robert Gibbs told reporters during his daily briefing.

Yet Obama is also scheduled to leave on a 10-day trip to Asia on Wednesday. Gibbs would not rule out delaying the trip so Obama could attend the service before setting off on the major international trip of the year.

Gibbs said the president's schedule remains in flux.

Obama ordered the flags at the White House and other federal buildings to be at half-staff until Veterans Day. He called it a modest tribute to those who were slain and to those who put their lives on the line in the armed services each day.

"We stand in awe of their sacrifice, and we pray for the safety of those who fight, and for the families of those who have fallen," he said.

The president promised that that his administration would update the nation as it learns more about what happened, and why, at Fort Hood.

The suspected shooter, Maj. Nidal Malik Hasan, was shot and remains hospitalized.