A suicide bomber on a bicycle killed 28 Iraqi policemen doing their morning exercises at their base north of Baghdad today, police said, in one of the deadliest strikes on security forces in months.
The bomber entered the base in the volatile Diyala province and blew himself up amidst members of a rapid reaction force, said Major-General Ghanim al-Quraishi, the Diyala police chief.
At least 20 people were wounded in the attack, including a woman and a child, police said.
No group claimed immediate responsibility for the Baquba bombing, but it bore the hallmarks of al Qaeda, which has often used suicide bombers in attacks on Iraqi security forces to devastating effect.
The base is in the city of Baquba, capital of Diyala province, a religiously and ethnically mixed region where al Qaeda and other Sunni Arab insurgent groups as well as Shia Muslim militias operate.
In other violence, a car bomb in a residential area in the northern Iraqi town of Siniya demolished two homes and killed four people and wounded 11, police and health officials said.
Al Qaeda has vowed to step up attacks on the security forces as well as Sunni Arab tribal leaders and Sunni insurgents who have allied themselves with US forces in Diyala, one of Iraq's most dangerous provinces, to root out the Sunni Islamist group.
US and Iraqi forces launched a major offensive against al Qaeda in Diyala in June, regaining control of Baquba and forcing many of the group's fighters to flee northwards, to Salahuddin and Nineveh provinces to regroup.
The US military has fostered the creation of what it calls "concerned citizens' groups" in Diyala.
These are modelled on tribal police units first formed in western Anbar, where tribal chiefs have joined forces with US forces to oust al Qaeda.
They include militants from Sunni nationalist insurgent groups such as the 1920 Revolution Brigades, which have distanced themselves from al Qaeda's hardline interpretation of Islam and indiscriminate killings of civilians.
Gunmen kidnapped 10 members of one of Diyala's tribal group fighting al Qaeda as they were returning to their hometown from Baghdad on Sunday, relatives said.
Baquba's police chief was among 26 people killed last month when a suicide bomber blew himself up in a mosque compound as local Shia and Sunni Arab leaders held reconciliation talks.
The US military has poured 30,000 extra troops into Iraq as part of President George W Bush's new Iraq strategy to create a more stable security environment for the country's feuding leaders to reconcile their warring sects.
Tens of thousands of Iraqis have been killed in sectarian violence between majority Shia and minority Sunni Arabs since February 2006, when bombers blew up a revered Shia shrine in the town of Samarra, north of Baghdad.
The second-ranking US general in Iraq, Lieutenant-General Raymond Odierno, said last week that the US-led crackdown had succeeded in reducing violence to its lowest levels since January 2006.