Iraqi security forces have found 53 corpses, blindfolded and handcuffed, in a town south of Baghdad.
Officials said that the bodies had been left in the mainly Shia Muslim village of Khamissiya early on Wednesday, about 25km southeast of the city of Hilla, near the main highway running from the capital to the southern provinces.
The head of the provincial council, the local police and the governor's office all confirmed the discovery of the bodies, but had no immediate information on the identity of the dead, who appeared to have been killed execution style.
Sunni fighters seized control of large parts of northern and western Iraq last month, sweeping towards Baghdad in the most serious challenge to the Shia-led government of Nouri al-Maliki, the prime minister, since the withdrawal of US forces in 2011.
Fierce fighting between the rebels and the army, backed by Shia armed groups, has raised fears of a return to the sectarian bloodshed which peaked in Iraq in 2006 and 2007.
Al Jazeera's Imran Khan, reporting from Baghdad, said that the incident could ignite more fears of sectarian violence.
"A lot of people are very nervous," he said. "What authorities are worried about now are revenge attacks."
Sunni fighters have been carrying out attacks around the southern rim of Baghdad since the spring.
In response, Shia militias have been active in the rural districts of Baghdad, abducting Sunnis they suspected of terrorism, many of whom later turn up dead.
According to medical officials, the number of unidentified bodies found around Baghdad has risen steadily since the beginning of the year.
Maliki calls Erbil a 'terror base'
Meanwhile, Maliki on Wednesday said the Kurdish-controlled city of Erbil was becoming an operations base for the Islamic State group that has seized areas of northern and western Iraq.
"We will never be silent about Erbil becoming a base for the operations of the Islamic State and Baathists and al-Qaeda and the terrorists," Maliki said in his weekly televised address.
Al Jazeera's Khan said that the statement was "out of the blue" and unexpected.
Maliki's relationship with Massoud Barzani, the Kurdish president, has deteriorated amid the sectarian fighting that has threatened to split the country.
Barzani last week asked the parliament of the autonomous Kurdish region to plan a referendum on Kurdish independence, signalling his impatience with Baghdad.
Maliki, meanwhile, has accused the Kurds of exploiting the crisis to push for statehood.