BAGHDAD – A female suicide bomber struck black-clad worshippers preparing for Shiite Islam’s holiest day, killing at least nine Wednesday in an attack that highlighted insurgents’ widening array of tactics against a U.S.-led offensive in key areas on Baghdad’s doorstep.

A witness said people shouted slogans against al-Qaida in Iraq as they carried the dead and wounded from the blast scene near a marketplace in Diyala province – a region of farmland and palm groves northeast of Baghdad that holds strategic havens for extremists.

Diyala is a main battleground for U.S. and Iraqi troops trying to overwhelm al-Qaida strongholds in the capital and elsewhere around the country.

Many extremists fled for safer ground before the new offensive began last week, reducing the expected threats from roadside bombs and ambush attacks. But insurgents left behind a more unconventional – but still deadly – landscape of booby traps and tripwire explosives.

The latest bloodshed also came from a new tactic that appears to be developing in Diyala: a woman suicide bomber.

The blast in Khan Bani Saad, a Shiite village nine miles south of Baqouba, was the fourth suicide attack by a woman in Iraq in three months. All have taken place in Diyala.

U.S. officials say this indicates the militants are running short of male volunteers. However, it could also be that al-Qaida in Iraq believes women are less likely to be searched and that explosives are easier to conceal under women’s clothing.

In Wednesday’s attack, the woman blew herself up about 50 yards from a mosque as Shiite men in black made preparations for a ceremony marking Ashoura, the holiest day in the Shiite religious calendar, according to residents and police.

The explosion took place about 8:30 a.m. near a market as vendors were opening their stalls. Khalaf Ibrahim, 35, said he was walking toward the market to open his cigarette stall when he heard the explosion.

“I rushed with other people to see what happened,” he said. “When I arrived, I saw pieces of flesh, two maimed legs, and blood stains on the ground.”

“The wounded were screaming for help, and I helped carry the wounded to the police cars waiting to take them to the hospital,” he continued. “Some people were shouting anti-al-Qaida slogans as they were carrying the wounded and the dead.”

Police and hospital officials, speaking on condition of anonymity because they were afraid of being attacked, said nine people were killed and six wounded. The U.S. military’s figures were seven dead and 15 wounded.

Sunni Arab militants have repeatedly targeted Ashoura processions, with hundreds killed by mortar shelling or car bombings since 2003. As a precaution, authorities announced a 48-hour ban on the use of vehicles in Baghdad and nine provinces south of the capital starting Thursday at dusk.

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.

The terrain in Diyala is far trickier for fighting insurgents and preventing attacks than the western desert of Anbar, from which U.S. forces and Sunni tribes ousted al-Qaida last year. Unable to fire at distant targets, the military must instead at times raid homes – some of which are booby-trapped.

There have been two such attacks in Diyala since the current military campaign was launched. Six American soldiers were killed and four were wounded Jan. 9, the second day of the operation. And on Monday, an explosion killed a police officer and two members of the local Awakening Council, a Sunni Arab group that switched sides to join U.S. forces against al-Qaida in Iraq.

Associated Press Writer Sameer N. Yacoub contributed to this report.