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BEIJING (AP) — Armed police will patrol schools in China's capital after a farmer attacked kindergarten students with a hammer, then burned himself to death Friday in the third classroom assault in as many days.

The government ordered schools across the country to tighten security, and anxious parents of students targeted in an earlier attack marched in protest Friday night, demanding a better government response to the crisis.

In the latest assault, Wang Yonglai used a motorcycle to break down the gate of the Shangzhuang Primary School in the city of Weifang and struck a teacher who tried to block him before hitting students with a hammer, the official Xinhua News Agency said.

Wang then grabbed two children, poured gasoline over his body, and set himself on fire. Teachers pulled the children to safety, but Wang died. None of the five injured students had life-threatening wounds, Xinhua said.

The attack was confirmed by an employee at the Weifang Public Security information office. Wang's motive was unclear. Xinhua described him only as a farmer.

Chinese schools have had five such attacks in just over a month — unusual in a country where extreme violence is comparatively rare and strict controls keep most people from owning guns. Sociologists suspect the rampages — usually by lone, male attackers — could be copycat actions.

State media reports have largely shied away from why students have been targets. Experts say outbursts against defenseless children can be due to social pressures in a rapidly changing society.

The attacks have been particularly shocking because most urban families in China have only one child due to government population control policies.

"Children are the ones people care about the most, and they are the most innocent," said Ma Ai, a sociology professor at the China University of Political Sciences and Law in Beijing.

Targeting children is "beyond the bottom line of human morals," he said.

State media either ignored or played down Friday's attack. It wasn't mentioned on the evening news in the eastern province of Shandong, where it occurred, and Xinhua didn't release a Chinese-language story on its website. Experts have worried openly about copycats, but authorities may also have wanted to avoid overshadowing Friday's opening of the World Expo in Shanghai, a pet government project.

"In circumstances like this, where it appears quite possible there's a copycat element, it's responsible for agencies to limit both the volume and the type of publicity," said Michael Phillips, the Shanghai-based co-author of a mental health survey in China published in the medical journal The Lancet in June.

On Wednesday, a 33-year-old former teacher broke into a primary school in the southern city of Leizhou and wounded 15 students and a teacher with a knife. The attacker had been on sick leave from another school since 2006 for mental health problems.

At a school in the eastern city of Taixing on Thursday, a 47-year-old unemployed man armed with an eight-inch (20-centimeter) knife wounded 29 students aged 4 or 5 — five of them seriously — plus two teachers and a security guard.

A group of parents marched Friday night outside the Taixing People's Hospital, demanding a better government response and proper care for their children. Video posted online showed them holding signs that read "Baby come home," and chanting, "We want the truth!"

Two witnesses, including a parent, confirmed the protest by phone and said police were at the scene. A photo posted online showed what looked like hundreds of people outside the hospital. Another showed broken glass on a sidewalk, describing it as the hospital entrance.

The same Twitter feed later showed a photo of city leaders meeting with parents and said they told the crowd that four people remained in grave condition.

The government on Friday issued an urgent directive to schools to tighten security. In the capital, the Beijing Education Commission ordered armed tactical police to begin patrolling around nursery, primary and secondary schools starting May 4, the first day back to school after the May Day holiday. Police will be on site when classes begin and end.

According to news reports, guards will be armed with police batons and pepper spray in a district of the eastern city of Nanjing, and guards at kindergarten, elementary and middle schools in one Beijing district have been given long-handled metal restraint poles with a hook on the end. In Jinan, the capital of the province where Friday's attack occurred, police posts are being built on elementary and middle schools campuses.

The Education Ministry's directive Friday, posted on its website, urged "concrete actions," including strictly implementing a rule already on the books to register all visitors to school campuses and preventing unidentified people from entering.

The order also told schools to work closely with police to "implement all kinds of security activities."

The central government first ordered increased school security in 2004 following an attack that left nine students dead at a Beijing school. Since 2006, schools have been required to register or inspect all visitors.

In an editorial Friday, the English-language China Daily said security should be tightened at schools nationwide, but it stressed the need to prevent attacks in the first place.

China likely has about 173 million adults with mental health disorders, and 158 million of them have never had professional help, according to a survey in four provinces published in The Lancet in June.

"It can be easy to put killers on trial and execute them, but it is far more difficult to find out the deep-seated causes behind such horrifying acts," the China Daily editorial said. "Our efforts should be focused on preventing these from happening. We should find out what propelled them to such extremes. What problems do they have? Could anyone have helped, especially the authorities?"

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Associated Press writer Cara Anna contributed to this story.