Captain Saed Ahmed said the bomb went off as people were emerging from the Great Prophet shrine in the town north of Baghdad.
He said nine people were killed and another 21 wounded in the Friday afternoon attack.
Earlier on Friday, at least two people were killed and 13 others wounded in an attack on a crowd of day labourers gathered at a Baghdad square, medics and security officials said.
Security sources said a group of armed men in a minibus opened fire on the labourers in the south-eastern al-Jadida district.
"The labourers were gathered at their meeting place when two cars drove up at 7.30 am (0330 GMT)," a police source said.
"They opened fire on the crowd."
The two cars then sped away from the scene. As they left they opened fire on a government vehicle travelling on one of eastern Baghdad's main highways, killing one man and wounding two more, police said.
Earlier, police sources said the third man was a transport ministry employee.
The morning attack followed a series of car bombings on Wednesday morning in the northern Baghdad district of Kadhimiyah against another group of day labourers.
Also in al-Jadida, police said a Shia cleric, Sheikh Fadel Alami, was killed in his car.
An Iraqi-US operation in Tal Afar
has triggered a violent backlash
South of Baghdad, a bomber killed three policemen and wounded six others after ramming his explosives-packed car into a police convoy on a highway near Hasswa, some 60km from the capital, police said.
And a senior regional official, Amer al-Khafaji, was assassinated along with four bodyguards in a night raid on his home in nearby Iskandariyah. Two other guards were wounded.
On Thursday, at least 25 members of an elite police commando unit were killed in three separate car bomb attacks in the southern Baghdad district of Dora.
In Baquba, north of Baghdad, another police commando was killed when a group of armed men attacked his unit, police sources said.
Four Iraqi soldiers were also killed when a roadside bomb struck their vehicle in the town of Khalidiya, west of Baghdad, policeman Mohammed Abbass said.
On Friday, the US military announced that a marine was killed near Ramadi, 110km west of Baghdad.
The soldier from the 2nd Marine Division was killed "from an indirect fire explosion" on Thursday, it said, using the normal term for a mortar attack.
The death brings to at least 1897 the number of American military personnel killed in Iraq since the US-led invasion of March 2003, according to Pentagon figures.
The Iraqi capital has witnessed a surge in attacks against Iraqi security forces, US military targets, and civilians since al-Qaida in Iraq leader Abu Musab al-Zarqawi declared all-out war against the Iraqi Shia community.
Al-Zarqawi warned Shia and
Sunnis ahead of the referendum
In an audio tape recording that has not yet been authenticated, al-Zarqawi said all Iraqis working with US forces and/or supporting the government of Prime Minister Ibrahim al-Jaafari would now become targets.
He also warned the Sunni community not to participate in an upcoming referendum vote.
On Thursday afternoon, Sheikh Mehdi al-Attar, a senior member of the al-Dawa party, was killed when his car was attacked by unidentified assailants in Hilla, 100km south of Baghdad.