A US soldier pleaded guilty Monday to killing five of his colleagues in Iraq four years ago, in a plea deal to escape a death sentence, a military spokesman said.

Army Sergeant John Russell was accused of the May 2009 killings at a clinic for soldiers suffering from war-related stress at Camp Liberty, the largest US base in Iraq.

Russell, who has previously denied responsablity, "said 'I killed these people,' he acknowledged that," said Gary Dangerfield, a spokesman for the Joint Base Lewis-McChord (JBLM), south of Seattle.

He added, however, that Russell has not admitted premeditated murder, which prosecutors have been trying to prove.

"He's just saying he murdered them. He didn't say it was premeditated, based upon his mental condition," Dangerfield told AFP.

"What we've agreed upon is the death penalty will be taken off the table, so that ... the maximum he will face is life in prison without parole," he said, adding the sentence will be decided at a court martial.

Russell, who has been held at JBLM in the northwestern US state of Washington, was present for Monday's plea hearing.

At the time, the Camp Liberty killings were the single deadliest toll on US forces in a month in Iraq, and came at a sensitive moment in the US military's occupation of the country it invaded in 2003 to topple Saddam Hussein.