BAGHDAD, Iraq - Insurgents dragged five Shiite Muslim schoolteachers and their driver into a classroom, lined them against a wall and gunned them down Monday — slayings in Iraq's notorious Triangle of Death that reflect the enflamed sectarian divisions ahead of a crucial constitutional referendum.

The shooting was a rare attack on a school amid Iraq's relentless violence, and it was particularly stunning since the gunmen targeted teachers in a school where the children were mainly Sunnis. Elsewhere Monday, a suicide attack and roadside bombings killed 10 Iraqis and three Americans, bringing to at least 52 the number of people killed in the past two days.

The Iraqi and U.S. governments have warned that Sunni Arab insurgents are likely to increase their attacks ahead of the Oct. 15 national referendum.

Shiite leaders have called on their followers to refrain from revenge attacks against Sunnis, fearing a civil war could result, though Sunnis have accused Shiite militias of carrying out some killings of Sunni figures.

But in one of the first public calls for individual Shiites to take action, a prominent Shiite cleric, Ayatollah Mohammed al-Yaaqubi, issued a religious edict Monday allowing his followers to "kill terrorists before they kill."

"Self-restraint does not mean surrender. ... Protecting society from terrorists is a religious duty," al-Yaaqubi said. He also called on Shiites to "deepen dialogue with Sunnis" who are not "terrorists or Saddamists."

Earlier this month, al-Qaida's leader in Iraq, Abu Musab al-Zarqawi, declared "all-out war" on Shiites and vowed to kill anyone participating in the referendum.

Leaders of Iraq's Sunni minority are calling on their followers to vote against the constitution and defeat a charter they believe will fracture the country and seal the domination of the Shiite majority.

American and Iraqi officials tried to rally Sunni support for the referendum by releasing 500 detainees from Abu Ghraib prison outside Baghdad to mark the coming Islamic holy month of Ramadan, a step called for by Sunni leaders.

U.S. defense officials in Washington said Monday that a leading deputy to al-Zarqawi, identified as Abu Azzam, was killed this weekend. The officials spoke on condition of anonymity, citing the sensitivity of the information.

CBS News, quoting   Pentagon officials, reported that U.S. forces killed Azzam in a house raid in Baghdad on Sunday. CBS described Azzam as Zarqawi's top deputy, in control of financing foreign fighters coming into Iraq.

It was unclear if Azzam was the same individual as a man whose name appeared in February on a U.S. list of the 29 most-wanted supporters of insurgent groups in Iraq. Sheikh Abdalluh Abu Azzam (aka Amir of Anbar) was listed as a Zarqawi lieutenant with a $50,000 award for his capture.

In the north, a top aide to al-Zarqawi surrendered to police in the city of Mosul, Iraqi army Brig. Gen. Ali Attalah said Monday. The aide, Abdul Rahman Hasan Shahin, was one of the most wanted figures in Mosul, Attalah said.

There have been few attacks on schools in Iraq, which have little protection — though children are constant witnesses to, and sometimes victims of, the violence.

Classes had just ended at the Al-Jazeera Elementary School in the village of Muelha, 30 miles south of Baghdad, when the shooting took place at about 1:15 p.m.

Police Capt. Muthana Khaled said that as five Shiite teachers got into a minivan to head home, two cars pulled up carrying gunmen wearing police uniforms as a disguise.

The nine gunmen forced the teachers and their driver out of the van in front of students who were milling outside the school. The attackers dragged the six men into an empty classroom, lined them against a wall and shot them to death, Khaled said. The gunmen escaped.

Muelha is a Sunni-majority community in a region of villages with mixed Sunni-Shiite populations. The mix has made the area south of Baghdad a tinderbox of frequent shootings and bombings, mostly by Sunni insurgents targeting Shiite civilians. As a result, the region is sometimes called the Triangle of Death.

In the same region, a suicide attacker detonated his car in a market in the town of Iskandariyah hours after the school shooting, wounding six people, Police Capt. Adel Ketab said. A day earlier, a bomb on a bicycle ripped through a market in Musayyib, just south of Muelha, killing at least six.

Farther south, gunmen on Monday assassinated a senior Shiite official from the Supreme Council of the Islamic Revolution in Iraq in the town of Qurna, near Basra, said Haytham al-Hussein, an aide to the leader of the party, one of the main factions in the government.

The gunmen kidnapped Azhar Qassem Abdul Wahid as he was leaving SCIRI headquarters, Police Cap. Mushtaq Kadhim said. His bullet-riddled body was found handcuffed and dumped by a roadside.

In other violence Monday, a suicide car bomber in Baghdad attacked a police checkpoint guarding the oil ministry and several other government buildings, hitting a private bus carrying 24 ministry employees to work, said police Capt. Nabil Abdel Qadir.

The blast killed at least seven policemen and three people on the bus and wounded 36 people, Qadir said

A roadside bombing in western Baghdad killed two American soldiers, and a third U.S. soldier was killed in a bombing about 50 miles southeast of the capital, the military said. The deaths raised to 1,917 the number of U.S. service members who have died since the Iraq war started in March 2003, according to an Associated Press count.

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Associated Press writers Robert Burns and Katherine Shrader in Washington contributed to this report.

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THE AMERICAN LEFT WANTS AMERICANS TO BELIEVE THAT AMERICA IS ALWAYS THE AGGRESSOR.

AMERICA WAS NOT THE AGGRESSOR IN VIETNAM.