A suicide car bomber blew himself up in front of a Baghdad police academy on Sunday, killing 15 people and wounding 21 others in the deadliest attack for weeks in the Iraqi capital, security officials said.
At least seven other people were killed in attacks elsewhere in Iraq.
"The suicide bomber blew himself up at the entrance of the police academy on Palestine Street," an interior ministry official said, putting the toll at 15 killed and 21 wounded. A police colonel confirmed the toll.
The ministry official said the assailant was at the wheel of a car bomb and most of his victims were students applying to join the police force.
Security forces armed with Kalashnikov assault rifles were deployed on the street where the bombing occurred, preventing most cars from entering as a truck sprayed water on the site.
Tow-trucks dragged the burned-out remains of two cars down the street and off through traffic, leaving behind another car with its windshield shattered.
It was the deadliest attack in Iraq since January 27, when a suicide bomber detonated an explosives-packed car outside a hospital in the Iraqi capital, killing 31 people.
Also on Sunday, gun and bomb attacks in other parts of the country killed seven people, among them four police informants, a policeman and two anti-Qaeda militiamen, and wounded four others, security officials said.
"A group of suspected Al-Qaeda gunmen attacked a house in the centre of Baquba around 7:30 am (0430 GMT)," a police major in Baquba, 60 kilometres (37.5 miles) north of Baghdad, said.
"The attackers killed three women and one man from one family inside the house," the major said, adding they were all police informants.
Gunmen in a civilian car also attacked a checkpoint manned by police and anti-Qaeda Sahwa (Awakening) militia members in Abu Khamis, north of Baquba, killing a policeman and two Sahwa members, a police lieutenant colonel said.
And two more Sahwa members were wounded by a roadside bomb near Samarra, 110 kilometres (70 miles) north of Baghdad, a lieutenant colonel in the Samarra police said.
The Sahwa are made up of Sunni tribesmen who joined forces with the US military against Al-Qaeda from late 2006, helping turn the tide of the insurgency.
Violence in Iraq is down from its peak in 2006 and 2007, but attacks remain common, killing 151 people in January.
A Baghdad military spokesman said earlier this month that the ranks of Al-Qaeda, for which suicide bombings are a favoured tactic, have thinned dramatically but the organisation remains a danger in Iraq.
"According to the numbers of our intelligence services, which are the same as those of the Americans, Al-Qaeda had 33,000 members in 2006. Today, they are no more than 3,000," Qassem Atta told Al-Sharq Al-Awsat newspaper.
"Despite this dramatic drop, Al-Qaeda remains a danger," he said.
Only two to three potential suicide bombers enter Iraq each month compared to 100 would-be martyrs in 2006, when sectarian violence killed on average 180 people per day, according to the same source.