BAGHDAD, Iraq (CNN) -- A female suicide bomber killed 16 people and wounded 40 Sunday when she detonated her explosives in a crowded area of central Baquba, police there said.
Police, women and children were among the casualties, according to the Diyala Military Operations command.
The attack happened near the main government complex in Baquba on a street that security officials had sealed off last week. Only official vehicles were being allowed in the area; civilian vehicles without special clearance were prohibited.
More than 20 female suicide bombers have carried out attacks in Iraq this year, a number much higher than in previous years. According to the U.S. military, women carried out eight bombings in 2007.
Authorities said that al Qaeda in Iraq is recruiting women and that increasing numbers of women are volunteering for missions.
The women are desperate and hopeless, officials said, and most have pre-existing ties to the insurgency. Their primary motive is revenge for a male family member killed by U.S. or Iraqi forces, the officials said.
"We do see certain members of cells attempting to persuade women -- specifically, in many cases, wives of those who have been killed as terrorists -- to conduct suicide operations," U.S. Maj. Gen. Mark Hertling said recently. His area of operations includes the volatile Diyala province.
Hertling's troops in Diyala have launched operations targeting relatives of suspected female bombers, as they attempt to break up the rings that are recruiting the women and girls.
Intelligence gathered from detainees indicates that al Qaeda in Iraq is looking for women with three main characteristics: those who are illiterate, are deeply religious or who have financial struggles.
Women in the last category often have money problems because they've lost the male head of the household, officials said.
Females always have played a role in the insurgency in Iraq, helping feed militants, hiding them in their homes and helping sneak weapons around the country.
They have proved to be effective in their operations because women are not to be searched by men for cultural and religious reasons.
The U.S. military has created a program called the Daughters of Iraq, similar to the U.S.-backed Sons of Iraq, across the Sunni regions of the country. The Daughters of Iraq are being trained to conduct searches of women.
In the northern city of Mosul, a suicide car bomber detonated near a police checkpoint, wounding at least 14 people -- including four policemen -- according to police.
Mosul is the capital of Nineveh province where Iraqi Prime Minister Nuri al-Maliki launched an ongoing offensive against al Qaeda in Iraq and other Sunni extremists last month.
Sunday's violence comes ahead of a U.S. report that will say violence in Iraq declined in the early part of this year, according to officials familiar with the report. The Pentagon's upcoming report to Congress, which could be released as early as Monday, will cover events in Iraq from mid-February to mid-May.
CNN's Jomana Karadsheh contributed to this report.