Iraqi police have found the bodies of 14 men, apparently the victims of execution-style killings, in Baghdad.
The victims are reported to have been shot in the head
They were found in shallow graves, blindfolded with their arms bound and with bullet wounds to the head - possible victims of revenge killings.
The grim find came as at least eight police officers died in a bombing near the northern city of Tikrit.
Later at least 16 people were killed and more than 40 injured in a suicide car bomb south of Baghdad.
The blast happened in a market in Suwayra, 60km (40 miles) south of the capital.
There has been intense violence since a new Iraqi government was announced in late April. More than 250 have died.
According to the Iraqi police, the graves in Baghdad were found when one of their patrols spotted two men digging a hole in wasteland on the outskirts of the city.
The men ran away when approached.
MAJOR ATTACKS SINCE JAN POLL
5 May: At least 23 people die in wave of attacks in Baghdad
4 May: At least 50 people killed in suicide attack on police recruits in Irbil
29 April: At least 29 people killed in wave of car bomb attacks on Iraqi security forces
10 March: 47 people killed by suicide bomber at Shia funeral in Mosul
28 February: Massive car bomb kills 125 people in Hilla
19 February: Suicide bombers kill 30 people during Shia Ashura celebrations
18 February: Around 29 people die in attacks in Baghdad and Iskandariya
7 February: Attacks on security forces kill at least 25 people in Mosul and Baquba
When the police investigated, they found they had been trying to bury two bodies. The bodies of 12 other men were later found buried in shallow graves nearby.
The bodies were dressed in long white robes, the traditional Arab garb favoured by Sunni Muslims.
The victims are believed to have been killed recently, said the interior ministry official.
The BBC's Jim Muir says the incident does not fit into the pattern of normal insurgent activity.
When the insurgents kill people they regard as collaborators, they publicise it, our correspondent says. Bodies are thrown in the street, often with signs attached to them, warning that others will share the same fate.
These bodies were found on the edge of an area heavily populated by Shia Muslims, who are frequently the victims of Sunni insurgents.
There is consequently speculation that these were revenge killings carried out against people suspected of being involved or having sympathy with the insurgents.
There have been other unofficial reports that such killings have been taking place.
Meanwhile, in the Tikrit blast, at least eight people were killed and several more were injured.
The incident took place at an army and police checkpoint north of the city at about 0800 (0400GMT).
The wounded include at least five police officers and two civilians.
Most of the casualties were believed to be on board aboard a minibus transporting policemen, which had stopped at a checkpoint.
At least one report says the bomb was hidden in the minibus itself. Other reports say a car bomber pulled up alongside the vehicle and detonated explosives.
The attack comes a day after at least 23 people were killed in suicide bombings and gun attacks on police and army targets in Baghdad. On Wednesday, at least 50 were killed in an attack on police recruits in Irbil.
Iraqi police and army forces have been a prime target of insurgents fighting against the US-led military presence in the country.
Prime Minister Ibrahim Jaafari is still trying to bring leading Sunni figures into the government in order to reduce support among Sunnis for the insurgency.
Key posts, such as the defence and oil ministries, remain vacant.
Many Iraqis are blaming the delay in forming a complete government for the apparently unstoppable wave of violence, our correspondent says.