Taipei (AFP) - A Taiwanese man suspected of decapitating a four-year-old girl was beaten by an angry mob, as the case sparked fresh debate Tuesday about the death penalty for child-killers.

The man grabbed the child as she cycled to a Taipei metro station with her mother on Monday, and beheaded her with a kitchen knife, police said.

The suspect pushed away the girl's mother as she tried to save her daughter. Seven bystanders were also unable to stop the man, police added.

The girl has been identified only by her surname Liu. Local media have used her family nickname "little light bulb".

Police said the suspect, a 33-year-old surnamed Wang, had previously been arrested for drug related crimes and had sought medical treatment for mental illness.

The case, the second child killing in Taipei in less than a year, has sparked widespread public anger and criticism of calls to abolish the death penalty.

Taiwan resumed capital punishment in 2010 after a five-year hiatus. Executions are reserved for serious crimes including aggravated murder and kidnapping, but the political elite is divided over whether or not to retain it.

Parliament says it will on Thursday a review of a bill that would ensure those convicted of killing children under 12 are given the death penalty, or at least a life sentence in the case of severe mental illness.

"I am deeply saddened by the case... (the suspect) should be sentenced to death in the case of a stranger killing a child," said lawmaker Wang Yu-min, who proposed the bill.

Children's welfare group the White Rose Social Care Association is planning to hold a rally in Taipei on April 10 to push for enforcement of capital punishment.

"This kind of random killing shows that Taiwan cannot afford to abolish the death penalty," said chairwoman Eva Liang.

The girl's mother, however, urged the public not to discuss the issue to allow the family time to grieve.

"If you are concerned about us or have sympathy, please respect us... I don't wish to see such discussions at the time being," she told reporters outside a funeral home, also asking people not to circulate photos of the girl's body.

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- 'Stop beating' -

Television footage Monday showed dozens of angry people gathered outside a police station in Taipei where the suspect was being held.

Some attacked the man as he was being transferred to the prosecutor's office for questioning. He pleaded with them to "stop beating".

Others came to lay flowers and toys at the spot where the girl was killed and her family held a religious ceremony for her there.

President-elect Tsai Ing-wen who will take office on May 20, also went to the scene to lay flowers.

"This incident deals a big blow to Taiwan's society. Many Taiwanese people are saddened and feel insecure... We should work together so parents don't have to worry and children can grow up safely," she said.