The blast occurred about 1 p.m. as dozens of people were leaving a walled compound that includes a courthouse and the provincial governor's office in Baqouba, capital of Diyala province and a former al-Qaida in Iraq stronghold 35 miles northeast of Baghdad.
A car bomb across the street from the same compound killed at least 40 people in April.
It appeared that the latest attack was timed to maximize casualties since many people were leaving the compound because the government offices there were to close soon for the day.
A U.S. military statement said the dead included seven Iraqi police and eight civilians. Ten police were among the wounded. Iraqi authorities said 16 people were killed and 42 wounded.
"I was trying to leave the court when the explosion took place," said one witness, who was wounded by shrapnel but refused to give his name because of fears for his own safety.
"I heard some of the injured people saying they saw a woman wearing a black robe blow herself up."
Al-Qaida has been increasingly using women because their black, billowing abaya robes easily conceal explosives. Iraqi police often lack enough policewomen to search women carefully.
The number of female suicide attacks has risen from eight in 2007 to 21 so far this year, according to U.S. military figures. Eight of the attacks were in Diyala province.
Last year, U.S. soldiers regained control of Baqouba, which had been declared the capital of the Islamic State of Iraq, an al-Qaida front organization. But the terror movement has been trying to regroup in the strategic Diyala province, which extends from the Iranian border to the eastern gates of Baghdad.
To the north, a roadside bomb Sunday apparently targeting a police patrol struck a civilian vehicle instead, killing four people, near Kirkuk, police reported. A suicide car bomber attacked a police checkpoint Sunday in the northwestern city of Mosul, wounding 14 people, including four policemen, provincial police said.
The violence occurred as U.S. and Iraqi authorities are trying to meet a July target date for completing a security agreement that would allow American troops to remain in the country after the U.N. mandate expires at the end of this year.
Talks bogged down over several key issues, which Iraqi lawmakers said violated the nation's sovereignty. Last week, however, Iraqi authorities said prospects for a deal had brightened after the Americans submitted new, unspecified proposals.
In Lebanon, however, the country's top Shiite cleric called Sunday on Iraqis to reject any deal that would allow the U.S. "to continue its occupation" and hijack the country's sovereignty.
"We specifically warn Iraqis not to submit to American temptation or pressures to sign an agreement with the Americans that will enable them to continue their occupation of Iraq under new slogans," Grand Ayatollah Mohammed Hussein Fadlallah said.
Fadlallah's remarks are significant because he is one of the founders of Iraqi Prime Minister Nouri al-Maliki's Dawa party and serves as the spiritual guide for many key Iraqi Shiite leaders.
Elsewhere Sunday, police said they have arrested six men suspected in the killing of the head of Saddam Hussein's tribe this month. Sheik Ali al-Nida, the head of Iraq's Albu Nasir tribe, and one of his guards were killed on June 10 when a bomb planted on their car exploded in Tikrit.
Police said three of those arrested were related to the sheik. Another was his longtime personal driver and trusted family employee, who police said accepted money to stick a bomb on the undercarriage of the victim's car.
Last year, al-Nida founded a so-called Awakening Council in Saddam's home village of Ouja, partnering with U.S. forces to fight Sunni militants in the area.
A police officer, who spoke on condition of anonymity because he wasn't authorized to release the information, said investigators suspected al-Qaida in Iraq was behind the attack as part of its campaign of violence against Sunni tribal leaders who have joined forces with the Americans.
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Associated Press writers Sameer N. Yacoub and Hamid Ahmed in Baghdad and Bassem Mroue in Beirut, Lebanon, contributed to this report.
