BAGHDAD (AP) — Men dressed as Iraqi soldiers abducted 18 Sunnis, whose bullet-ridden corpses turned up in farmland just south of Baghdad, authorities said Friday, a grim reminder of the worst days of sectarian killings that plagued the country after the U.S. invasion.

Police said officers later discovered the beheaded corpses of three men in Baghdad's eastern suburbs, their hands tied behind their backs, part of attacks that killed 25 others Friday. The apparently targeted killings come after similar killings earlier this week, raising fears that the country, already embroiled in months of rising violence, could see the return of Shiite and Sunni Muslim death squads roaming the streets.

"These recent killings show that the fears by many Iraqis that their country is heading to darker days similar to 2006-2007 are true and that the wounds of the past are not healed yet," Baghdad-based political analyst Hadi Jalo said. "If the government does not take effective measures to stop the sectarian tension and security deterioration, I think that we should expect more such killings."

Authorities found the bodies early Friday in farmland near the Sunni town of Mishahda, some 30 kilometers (20 miles) north of Baghdad. Gunmen in four cars abducted the men, who included two army officers, a local Sunni tribal sheik, the sheik's son and Mishahda's mayor, from their homes late Thursday.

Police later said it appeared the men were killed by gunshot wounds to the head. A Baghdad morgue official confirmed receiving the 18 bodies. He said that all the relatives who came forward to claim the bodies were Sunnis.

It wasn't clear who rounded up and killed the men. Shiite militiamen could be seeking revenge for the ongoing Sunni insurgent attacks against Shiite neighborhoods. Militants with al-Qaida's local branch targets Sunnis in attacks as well and once took control of a town west of Baghdad two years ago by dressing as police officers and driving around in real squad cars. It also could be a personal vendetta.

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The killings come after police officers found the bodies of 13 men Wednesday in two locations around Baghdad, all killed by what appeared to be close-range gunshots. Some had their hands and feet tied.

Since late December, Iraq's minority Sunnis has been protesting what they perceive as discrimination and tough anti-terrorism measures against them by the Shiite-led government. The Sunni attacks followed a government crackdown on a Sunni protest camp in the northern town of Hawija in which 44 civilians and one member of the security forces were killed, according to U.N. estimates. More than 5,500 people have been killed since the crackdown.

Now some call for Shiites to create armed "popular committees," attached in some form to the regular security forces. The idea raises the specter of some of Iraq's darkest years following the 2003 U.S.-led invasion that toppled Saddam Hussein's Sunni-led regime, paving the way for long-repressed majority Shiites to seize power.

Iranian-backed Shiite death squads roamed Baghdad from 2006-2008, killing Sunnis by the dozens and dumping their often mutilated bodies on the streets or in the river in retaliation for the devastating bombings and suicide attacks blamed on Sunni insurgents. Sunnis also formed their own death squads for revenge killings.

Meanwhile Friday, violence raged on elsewhere in Iraq. A bomb exploded inside a sheep market in Baghdad's southeastern suburb of Nahrawan, killing three and wounding six, police said. In the western Abu Ghraib suburb, a roadside bomb killed one and wounded five, authorities said. Also, police said gunmen killed a government employee in a drive-by shooting in western Baghdad.

A bombing near a soccer field in Baghdad's southwestern suburb of Radhwaniy killed five people and wounded six, police said. Gunmen carrying guns fitted with silencers broke into a house in Ghadeer neighborhood, killing six women police described as prostitutes. Bombs stuck to cars killed a government employee and a city employee around Baghdad, authorities said.

Near the northern city of Mosul, a roadside bomb killed the mayor of Hamam al-Alil, police said. In Mosul, gunmen shot dead a government employee, authorities said. Police said gunmen also broke into a house and killed a man and his wife in the town of Sinjar, 400 kilometers (250 miles) northwest of Baghdad.

Medical officials confirmed the causality figures in the attacks. All officials spoke on condition of anonymity because they were not authorized to talk to journalists.