A suicide bomber on a bicycle killed 28 policemen at their base in the volatile Iraqi province of Diyala on Monday, police said, in one of the deadliest strikes on Iraq's security forces in months.
The bomber entered the base and attacked a group of policemen -- members of a rapid reaction force -- doing their morning exercises, said Major-General Ghanim al-Quraishi, police chief of Diyala province.
He said details of the bombing were confused because everyone at the scene had been killed or badly wounded.
The base is in the city of Baquba, capital of Diyala province, where al Qaeda and other Sunni Arab insurgent groups as well as Shi'ite Muslim militias operate.
At least 20 people were wounded in the attack, including a woman and a child, police said.
A car bomb in a residential area in the northern Iraqi town of Siniya demolished two homes and killed seven people and wounded 11, police and health officials 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 devastasting effect.
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 province to try to root out the Sunni Islamist group.
U.S. and Iraqi forces launched a major offensive against al Qaeda in Diyala province in June, regaining control of Baquba and forcing many of the group's fighters to flee elsewhere.
That led to the creation of "concerned citizens's groups" modelled on the tribal police units first formed in western Anbar, where tribal chiefs have joined with U.S. troops to force al Qaeda from the province.
Al Qaeda, however, has proved resilient and U.S. military commanders warn that it still retains the capability to launch devastating attacks.
Baquba's police chief was among 26 people killed last month when a suicide bomber blew himself up in a mosque compound where local Shi'ite and Sunni Arab leaders were holding reconciliation talks.
The U.S. 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 Shi'ites and minority Sunni Arabs since February 2006, when bombers blew up a revered Shi'ite shrine in the town of Samarra, north of Baghdad.
The second-ranking US general in Iraq, Lieutenant-General Raymond Odierno, said last week that violence had dropped to its lowest level since January 2006.
(Additional reporting by Aseel Kami in Baghdad)