BAGHDAD — The killers came at night, speaking passable English and wearing uniforms and carrying weapons that resembled those of the American military.

By the time they left the village of Hawr Rajab on Friday evening, they had fatally shot or slit the throats of 25 members of an extended family, Iraqi officials said Saturday, in a chilling episode of violence reminiscent of the worst days of the country’s sectarian warfare in 2006 and 2007.

Most of the 19 male victims were members of Iraqi security forces or of Awakening Councils, groups that now partner with American forces and are employed by the Iraqi government to protect Sunni neighborhoods, but whose members had once been allied with Sunni extremist groups like Al Qaeda in Mesopotamia during fighting against American troops.

Members of Awakening Councils are often branded by Al Qaeda as traitors, but their families have typically not been attacked. The Iraqi authorities said 25 people had been arrested as part of the investigation into the killings, including some who lived near the families.