President Barack Obama said he is "shocked and deeply saddened" by news that a US soldier opened fire at a counseling center, killing five fellow soldiers.
The president met with Defense Secretary Robert Gates on Monday to be briefed on the shooting at a sprawling US base on the western edge of Baghdad and adjacent to a facility Obama visited last month.
"I was shocked and deeply saddened to hear the news from Camp Victory this morning, and my heart goes out to the families and friends of all the service members involved in this horrible tragedy," Obama said in a statement.
"I will press to ensure that we fully understand what led to this tragedy, and that we are doing everything we can to ensure that our men and women in uniform are protected as they serve our country so capably and courageously in harm's way," he said.
It was unclear what provoked the shooting at a stress-counseling clinic. US officials said the soldier was in custody but gave no further details.