Authorities found the bodies Friday of 25 people, most of them kidnapped by men in army uniforms, and attacks killed 10 more, in scenes harkening back to Iraq's sectarian war.
The killings come amid a surge in violence that has seen victims snatched from their homes, only for their corpses to be found later, fuelling fears Iraq is slipping back into the worst of the bloodshed that plagued it from 2005 to 2007.
More than 6,000 people have been killed this year, forcing Baghdad to appeal for international help in battling militancy just months before a general election, as official concern focuses on a resurgent Al-Qaeda emboldened by the war neighbouring Syria.
Early Friday, authorities discovered the bodies of 18 men, including two tribal chiefs, four policemen and an army major, dumped in farmland near the Sunni Arab town of Tarmiyah, just north of Baghdad.
All of them had been shot in the head and chest, police and a medical source said.
The kidnappers, wearing military uniform and travelling in what appeared to be army vehicles, abducted the men early Friday, telling their families the men were suspects in various cases and were being taken for questioning.
Their bodies were found hours later, the sources said.
There was another such incident in Salaheddin province, north of Baghdad. Seven men -- all maintenance workers and labourers at a local football field -- were found dead, their throats cut.
A police officer told AFP he had felt physically sick while taking photographs of the mutilated corpses.
The brutal killings come just days after authorities discovered the bodies of 19 people shot dead in various parts of Baghdad, including eight found blindfolded and six whose corpses were left in a canal.
At the peak of sectarian fighting in the wake of the 2003 US-led invasion, Sunni and Shiite militias regularly carried out tit-for-tat kidnappings and assassinations and left scores of corpses littering the streets.
Many of the bodies were blindfolded and showed signs of torture.
Elsewhere in Iraq on Friday, attacks in and around Baghdad, and the predominantly Sunni cities of Mosul, Baquba and Kirkuk killed 10 people and wounded 19, officials said.
The capital and Sunni Arab parts of northern and western Iraq have borne the brunt of the recent upswing in bloodshed.
The violence worsened sharply after security forces stormed a Sunni protest camp in northern Iraq in April, sparking clashes in which dozens of people died.
The authorities have made some concessions aimed at placating the protesters and Sunnis in general, including freeing prisoners and raising the salaries of anti-Al-Qaeda Sahwa fighters.
At the same time, the security forces have trumpeted operations targeting militants.
But daily attacks have shown no sign of abating, with Friday's killings capping a week in which nearly 200 people have died nationwide.
Diplomats, analysts and rights groups say the government is not doing enough to address Sunni disquiet over what they see as mistreatment at the hands of the Shiite-led authorities.
On Wednesday, the UN Security Council condemned the violence and voiced support for government efforts to tackle the bloodshed.
Prime Minister Nuri al-Maliki used a recent trip to Washington to push for greater intelligence sharing and the timely delivery of new weapons systems in a bid to combat militants.