BAGHDAD – Iraqi officials are investigating claims that detainees, believed to be mostly Sunnis, were tortured at a makeshift prison in Baghdad, in a case that has outraged the country’s Sunni minority, Iraqi officials said Thursday.

The deputy human rights minister, Kamil Amin, said that three army officers have been arrested in connection with the case. An Iraqi who said he was in the prison described being beaten, tortured with electric shock treatment and smothered with a plastic bag.

The case, which was first reported Monday by the Los Angeles Times, has angered the country’s Sunni population who see it as another example of persecution by Iraq’s Shiite-led government.

The charges come at a delicate time, as the country waits to see who will take the lead in forming the next government: a coalition with extensive Sunni support, or a Shiite-dominated bloc led by the current prime minister.

The incident also raises chilling comparisons with the revelation in 2005 of a secret prison run by the Shiite-dominated security forces in Baghdad where Sunnis were tortured.

In the ensuing years of sectarian battles in the capital, Sunnis repeatedly accused security forces of actively aiding, or at least turning a blind eye to Shiite death squads.

At least 431 Iraqi men from the northern province of Ninevah were arrested last year and taken to a Ministry of Defense facility in Baghdad, said Amin. The Human Rights Ministry became involved after hearing complaints from family members of detainees saying they were tortured.

A former prisoner, Radhwan Shihab Ahmed Salih al-Abadi, said Thursday that he was arrested in December and taken to the prison where he was treated in a “barbaric way.”

“They used to asphyxiate us with plastic bags until we were about to fall unconscious and then open the bag,” he said. “They were also using electric shocks during investigation.”

Al-Abadi said he was arrested along with his brother, who was accused of being part of the insurgency and is still being held.

An army officer who worked at the prison said it was a military barracks that was converted into a detention facility last fall to hold the prisoners from Ninevah province, and that it has since been closed.

It was unclear exactly how much oversight there was of the facility although Amin said prisoners had access to judges and their families.