The Department of Home Affairs, which oversees immigration detention, confirmed the death of the man on Sunday.

"The department and Australian Border Force express our condolences to the man's family and friends," a Home Affairs spokesperson said.

"The matter has been referred for investigation to the appropriate agencies, including the NSW Coroner.

"As this matter will be subject to ongoing investigation, it would not be appropriate to comment further."

The Refugee Action Coalition were alerted to the death early on Sunday morning, with the Iraqi detainee in his 30s found dead in his cell.

The man is believed to have been last seen alive at 10pm on Saturday in his cell. He was a detainee for five years.

"It is shocking that there has been yet another suicide in Villawood detention centre," the coalition's spokesman Ian Rintoul said.

"It is not just a factory for mental illness, it is becoming a suicide factory."

The coalition says the man had asked to be moved several times at the centre because of tensions with other detainees, including a fight with another man on Saturday night.

Immigration detainees have access to health services, including mental health services.

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Australian Associated Press