Iraqi officials say a suicide bomber on a bicycle has killed at least 29 people at a police base in Baquba, north of Baghdad.
The bomber struck Monday morning as police recruits gathered for a training session. Twenty other people were wounded in the attack.
Baquba is the capital of Iraq's Diyala province, where Sunni Arab tribesmen and militants have joined U.S. and Iraqi forces in fighting al-Qaida in recent months.
Also Monday, the Iraqi Defense Ministry said a group of sheikhs from Diyala has been rescued after being taken hostage on Sunday. The Sunni and Shi'ite tribal leaders, who are part of a group that opposes al-Qaida in Iraq, were kidnapped in Baghdad after they met with a government official.
There are conflicting reports about the number of sheikhs who were kidnapped and rescued, and whether all survived the abduction.
The United States accuses a Shi'ite militia leader with links to radical Shi'ite cleric Moqtada al-Sadr's Mahdi Army of the kidnapping.
Iraq's Defense Ministry did not provide further information about the abductions or the rescue mission.
In other developments, Iraqi officials found 20 headless bodies dumped near Baquba.
Also, the U.S. military handed over security responsibilities in the mostly Shi'ite province of Karbala to Iraqi authorities. It is the eighth of Iraq's 18 provinces returned to Iraqi security control.
Karbala is home to the shrines of two revered Shi'ite imams, Imam Hussein and Imam Abbas. In August, clashes in the city between rival Shi'ite fighters killed at least 52 people during a major religious festival.
In other news Monday, a U.S. brigadier general, Jeffrey Dorko, was wounded in a roadside bombing in northern Baghdad. A military statement says he suffered non-life threatening injuries and was evacuated to Germany.
Some information for this report was provided by AP and Reuters.