A police official and eyewitnesses said a Shiite participating in the rites noticed a stranger in the crowd heading for the mosque, and tried to talk to him. The Shiite grabbed the man as he tried to enter the mosque and shouted "Stranger! Stranger!" At that point, the stranger detonated his explosive belt.
A Shiite witness, who would identify himself only as Abu Mohammed for fear of being attacked, said he was standing near the mosque watching the performing of the rites for the Ashoura ceremony.
"Suddenly I heard a big explosion and saw the people running in all directions," he said. "Minutes later, some came back to the site to search for relatives or their children. There were several bodies and wounded people on the ground."
The bombing killed 11 people, excluding the attacker, and wounded 15, according to an official at Baqouba General Hospital who spoke on condition of anonymity because he was not authorized to release the information.
Sunni Arab militants have repeatedly targeted Ashoura processions, with hundreds killed by mortar shelling or car bombings since 2003. Ashoura, which comes later this week, commemorates the death in a 7th century battle of Imam Hussein, one of Shiite Islam's most revered saints. His tomb is in Karbala, about 60 miles south of Baghdad.
Wednesday's bombing took place in Khan Bani Saad, a Shiite village nine miles south of Baqouba. A female suicide bomber struck black-clad worshippers preparing for Ashoura, killing at least nine people in an attack that highlighted insurgents' widening array of tactics against a U.S.-led offensive in key areas on Baghdad's doorstep.
Diyala has eluded the nationwide trend toward lower violence over the past six months. At least 273 civilians were slain in Diyala last month, compared to at least 213 in June, according to an Associated Press count. Over the same span, monthly civilian deaths in Baghdad dropped from at least 838 to at least 182.
The decline in violence has coincided with last year's buildup of American troops in Iraq, along with the emergence of largely Sunni groups fighting al-Qaeda in Iraq as well as a cease-fire by radical Shiite cleric Muqtada al-Sadr's Mahdi Army militia.
The additional troops were intended in part to reduce the bloodshed, thus giving the embattled government of Prime Minister Nouri al-Maliki breathing room to pursue national reconciliation among the country's Shiites, Sunni Arabs and Kurds.
The Kurds are a key group within the national governing coalition and have been Washington's most reliable allies in Iraq. Since the ouster of Saddam Hussein they have forged a close relationship with the majority Shiites.
But assertive acts by the Kurds, such as their insistence on cutting their own oil deals and refusal to fly the Iraqi national flag in the region, have irritated the Shiite-dominated government in Baghdad as well as Sunni Arabs. Many see such moves as a threat to the country's national unity.
The Iraqi Oil Ministry has decided to stop cooperating with international oil companies participating in production-sharing contracts with the Kurdish regional administration in northern Iraq, an official said Thursday.
The decision is considered a first step toward implementing the ministry's threats to blacklist and exclude these companies from any future deals with Baghdad if they refuse to abandon their oil deals with the self-ruling Kurdish government.
Four companies are thought to have agreements with both Oil Ministry and with Kurdistan: the United Arab Emirates' Crescent, Canada's Western Oil Sands and Heritage Oil, India's Reliance Industries and Austria's OMV.
A spokeswoman for Reliance Industries, who declined to be named, said the company has not received any official communication from the Iraqi government. She said the firm hoped any possible issues will be resolved without affecting business.
The Oil Ministry's decision came days after 145 Iraqi Arab lawmakers from rival sects joined forces to criticize what they claim is overreaching by the Kurds, alleging the powerful U.S.-backed minority's go-it-alone style threatens national unity. They took issue with Kurdish ambitions in the disputed northern city of Kirkuk and in negotiating deals with foreign oil companies without involving the central government.
With the national oil and gas law stuck in dispute between the Kurds and Arab leaders over who has the final say in managing oil and gas fields, the Kurds have signed 15 production-sharing contracts with 20 international oil companies. The Oil Ministry considers those contracts illegal.