A suicide bomber has killed at least 15 people in the Iraqi city of Falluja by blowing himself up in a crowd of men waiting to join the police.
Men waiting to sign up to the police are regular targets for attacks
The deaths are among dozens in the last 24 hours as insurgency and sectarian unrest grips the troubled country.
The bullet-riddled bodies of 14 men were recovered together in the Shaab district of the Iraqi capital Baghdad.
Four Shia students were pulled from a minibus and shot dead overnight. About 20 other corpses were found in Baghdad.
In another incident, a US contractor's car was hit by a roadside bomb near the southern city of Nasiriya, killing a civilian and two others in the vehicle.
The victims' nationalities were not immediately known.
Thirteen of the dead in Falluja were police recruits and two were serving officers, Iraqi officials said.
They said 30 people were wounded in the blast.
The bomber was dressed in civilian clothes and detonated his bomb outside the entrance of a police building.
Falluja lies about 50 km (30 miles) west of Baghdad in the mainly Sunni Arab province of Anbar, which has been a stronghold of the insurgency.
Sectarian violence has soared since the bombing of a revered Shia shrine in February. The US military estimates attacks on civilians have doubled.
But anti-US insurgents have also increasingly turned their fire on Iraq's new security forces in the three years since the US-led invasion of the country.
Signs of torture
The identities and sectarian affiliations of the 14 bodies discovered in Shaab are as yet unknown.
But they were young men aged between 20 and 30, they were blindfolded, bound and showed signs of torture - the hallmarks, according to the BBC's Jim Muir in Baghdad, of a sectarian attack.
Our correspondent says that many of the victims of massacres of this type have been Sunnis, some of them picked up by death squads which the Shia-controlled interior ministry is accused of allowing to operate under its cover.
But he says it is certainly not a one-way process - most of the victims of the Sunni-based insurgency have been Shia.
Iraq has seen a surge in violence in recent weeks
The four students died in al-Dura district after gunmen stopped a minibus full of young people being taken to a Baghdad college, interior ministry officials said.
"They pulled four students out of the bus and shot them dead," an official said.
Breaking the cycle of sectarian revenge killings will be one of the first and biggest challenges facing the new Iraqi government which is currently being put together, our correspondent says.
There is much debate over who should be in charge of the interior and defence ministries. It looks unlikely that they will again be put in the hands of people connected to the big factions and militias, he says.
Parliament is meanwhile meeting for only the third time since elections last December. MPs are expected to discuss setting up a committee to review the country's constitution.
The biggest Sunni Arab group in parliament, the Iraq Consensus Front, has said one of its members should head the constitutional committee.