This is very sad to hear about this.
BAGHDAD — The United States military said Monday that five American soldiers had been shot to death by a fellow soldier who opened fire on them at one of the biggest American bases in Baghdad, and that the suspected shooter was in custody.

The killings appeared to be one of the worst cases of lethal non-combat casualties for the American forces in Iraq since the invasion more than six years ago.

The shooting took place at around 2 p.m. local time at Camp Liberty, a sprawling base next to Baghdad airport, the military said in a statement. The names of the dead soldiers were being withheld pending family notification, the statement said.

“Anytime we lose one of our own, it affects us all,” Col. John Robinson, a spokesman for the U.S. military in Iraq, said in the statement.

CNN, citing unnamed officials, said that at least three others were wounded in the attack, which it said had taken place at a clinic for soldiers suffering from war stress.

Violence has dropped sharply in Iraq, but a rash of major bombings by insurgents has raised questions about security less than two months before American forces are due to withdraw combat troops from urban bases.

Earlier this month, two American soldiers were killed by a man wearing an Iraqi Army uniform at an Iraqi military training centre south of Mosul

In April, 18 American military personnel members were killed in Iraq — double the number in March and the highest since September 2008, when 25 were killed.