Thwarting security measures set up to protect a police recruiting center already hit by vehicle bombs, an attacker wearing explosives walked into the midst of a group of men applying for police jobs Saturday and detonated his charge, killing himself and at least 12 others, police and witnesses said.

The 9 a.m. attack on the police commando base in Baghdad's Yarmouk district "was not very loud. It sounded like the explosion of a tire," said Mays Naib, 32, who lives nearby.

Police initially put the death toll at 20, but the number was revised downward to 12, said police Col. Adnan Abdul Rahman, an Interior Ministry spokesman. He said 14 people were wounded.

Over the course of a nearly two-year-old insurgency in which assaults on Iraqi and U.S. security forces have been frequent, attackers repeatedly have targeted places where men stand in line to apply for jobs with the police and Iraqi army. Because would-be recruits typically are made to wait outside fortified bases and recruiting centers, they have proved to be easy targets for often-deadly bombings.

After previous attacks on the base in Yarmouk, the surrounding street had been blocked to provide greater security, Naib said. "So they send a suicide bomber to do this attack. Because of this recruiting center, we feel like we live in a battlefield," she said.

Despite the dangers that the job-seekers pose to the neighborhood, Naib said she felt sorry for "those poor people."

"What are they supposed to do?" she said. "They came here to look for a job and protect the country. Isn't that better than being without a job and turning to crime to make money to live?"

The dead and wounded were carried to Yarmouk Hospital, a few hundred yards from the attack. Outside the hospital, Khalid Hamza, 42, was trying to find a friend who had come to Baghdad from the southern town of Hilla to find work with the police. "His father is an old man; that is why he decided to join the police," Hamza said. "He did not tell his mother that he is going to join the police. She would never let him do that."

Al Qaeda in Iraq, the guerrilla organization led by Abu Musab Zarqawi, asserted responsibility for the bombing in a statement posted on the Internet. The authenticity of the claim could not be verified.

Meanwhile in Hilla, a mostly Shiite city 60 miles south of Baghdad, a suicide bomber detonated a belt of explosives at a police checkpoint in the city center, killing six policemen and the attacker, said Police Capt. Muthana Khalid Ali, according to the Associated Press.

About 10 minutes later, a second attacker blew himself up in a crowd of police officers and civilians who had rushed to the scene of the first blast, Ali said. Twenty-six people were injured, the AP reported. There was no immediate assertion of responsibility for either attack in Hilla.

On Friday, Zarqawi's radical Sunni Muslim group claimed to have carried out the drive-by shooting of a prominent Shiite Muslim cleric, Kamaleddin Ghuraifi, on a street in central Baghdad. On Saturday, a bomb exploded at a police checkpoint in Mahmudiyah, 15 miles south of Baghdad, shortly after Ghuraifi's funeral procession had passed by, according to the Reuters news agency.

The bomb, which police said was hidden in a vegetable cart, killed five people and wounded 12. It was not clear whether the bomb had been intended to hit the procession, which was taking Ghuraifi's body to be buried in the holy city of Najaf, 90 miles south of the capital.

Ghuraifi had been a Baghdad representative of Grand Ayatollah Ali Sistani, Iraq's most prominent Shiite religious leader, who has his headquarters in Najaf. On Saturday, the walls around Najaf's ornate Imam Ali shrine were filled with banners denouncing the recent assassinations of prominent Shiite religious and political figures and blaming them on Sunni insurgent groups. One of the banners demanded: "Can't the Sunni wise men stop the criminals?"

Meanwhile, another influential Shiite cleric's top lieutenant was released from detention Saturday after a year in U.S. military custody. The Najaf office of Moqtada Sadr, the rebel cleric whose militia twice battled U.S. forces last year, announced that Muhammed Tabatabei had been freed from Abu Ghraib prison, where he had been held without being charged. Tabatabei returned to Najaf, where he met with Sadr, the announcement said.

Special correspondent Saad Sarhan in Najaf contributed to this report.

Iraqis hold photos of Kamaleddin Ghuraifi at his funeral in Baghdad. Ghuraifi, a Shiite who was an aide to Grand Ayatollah Ali Sistani, was killed Friday.