BAGHDAD, Iraq — An aide to Grand Ayatollah Ali al-Sistani, Iraq's leading Shiite Muslim cleric, was assassinated yesterday in central Baghdad in the latest attack on leaders of Iraq's Shiite majority.

And early today, a suicide bomber strapped with explosives killed 20 people waiting outside a police recruiting center in Iraq's capital, an Interior Ministry spokesman said.

The attacker wore an explosive-laden belt and blew himself up outside the recruiting center in west Baghdad's Yarmouk neighborhood, said police Col. Adnan Abdul Rahman, an Interior Ministry spokesman. Most of those killed were recruits, he said.

Yarmouk Hospital received at least 17 bodies and treated 21 wounded, emergency room Dr. Muhanad Jawad said.

Insurgents bent on destabilizing Iraq's government frequently target security forces and recruiting centers where long lines form outside.

The cleric's aide killed yesterday, Kamal al-Deen al-Ghuraifi, was walking from his home to the Al-Karkh mosque to give a sermon. But before the imam could get there, a car sped up the wrong side of the road. Four men with Kalashnikovs leaned out the window and sprayed him and his guards with bullets, said Police Maj. Abdul Wahab Ahmed, the officer in charge of the investigation.

Al-Ghuraifi died instantly from the four bullets. His bodyguards were injured; one was his son.

Forty minutes later and about 55 yards up the road, a group of gunmen stormed into the Sunni mosque Saad Bin Abi Waqas. As Sheik Amer al-Tikriti began his sermon, they dragged him from the pulpit and kidnapped him.

"It was one man for one man," Ahmed said.

Al-Ghuraifi was the sixth representative of al-Sistani's to be killed in Baghdad since the new government took office April 28, according to al-Sistani's office in Najaf.

The seemingly eye-for-eye actions reflected the growing sectarian violence and political tensions in the nation.

In further violence, a car bomb exploded outside of Prime Minister Ibrahim al-Jaafari's Dawa party office, killing one bystander and injuring another.

"Terrorists are trying to create sectarian sedition here in Iraq by killing the religious figures from both the Sunnis and the Shiites," said Haitham al-Husseini, a spokesman for Abdul Aziz al-Hakim, a leader of the Shiite political party the Supreme Council for Islamic Revolution in Iraq.

Meanwhile, Sunnis have threatened to boycott the constitutional committee if their list of names to participate in drafting the constitution isn't approved soon, said Saleh al-Mutlak, of the Sunni National Dialogue Committee. Al-Mutlak is on the list submitted to help write the constitution. Sunni participation in writing Iraq's constitution is considered key to getting the document accepted by the Sunni minority, from which most of Iraq's insurgents have come.

Also yesterday, wide swaths of the capital were without drinking water for the second time in two weeks. A fire at a purification plant in Tarmiyah, just north of Baghdad, caused the water shortage, according to the Interior Ministry. It's unclear how the fire started.

In other violence, a political satirist on the government-owned Iraqia television station was killed in Mosul.

Police found Khaled al-Attar's body riddled with bullets, said Ghazi Faysal, the manager of the Iraqia network in the north.

U.S. and Iraqi military forces continued yesterday to try to drive insurgents out of towns in western Iraq. About 1,000 U.S. Marines, soldiers and sailors and 100 Iraqi troops conducted a fourth day of search operations in the town of Hit, about 95 miles northwest of Baghdad. The Marines said the push was meeting little resistance.

Less than a mile north of Hit, the statement said, Marines and sailors found 15 roadside bombs — 13 of them placed along an 800-yard stretch of road. "The insurgents had attempted to attach several of the bombs together in order to make a larger explosion and increase the blast radius of the bombs," the statement said.

In Ramadi, a city 60 miles west of Baghdad, residents directed police to a spot where the bodies of three men — described as a Saudi, a Jordanian and a Kuwaiti — had been dumped out of a pickup, according to Iraqi army 1st Lt. Hussein Fadhil Alwan. The residents said the dead men were members of al-Qaida in Iraq, the guerrilla group led by Abu Musab al-Zarqawi.

Later, a statement posted at a mosque in Ramadi by al-Zarqawi's group accused a local tribe of the killings: "We promise a fast and very swift punishment for this tribe because of what they did. They are apostates from Islam — they should be killed."

Also yesterday, Iraq's chief U.N. delegate accused U.S. Marines of killing his unarmed young cousin in what appeared to be "cold blood" and demanded an investigation and punishment for the perpetrators.

Compiled from Knight Ridder Newspapers, The Washington Post and The Associated Press