Three police officers and four other people have been convicted of torturing suspects to obtain confessions, China's official state news agency reported, in a rare instance of prosecution of the practice.

One of the cases resulted in the death of a man who was tortured with electric shocks and hit on the head and face with a shoe, Xinhua News Agency said Sunday. Mustard oil was poured into suspects' mouths in other forms of torture, it said.

The seven cases happened in March 2013 at the Daowai district police sub-bureau in the northeastern city of Harbin. Three police officers and four people hired by police to help with the investigations were convicted and given prison sentences of up to 2 1/2 years, it said.

Chinese authorities have said that the problem of torture and coerced confessions has been effectively addressed by measures introduced in the last five years, including physically separating interrogators from suspects, video recording of interrogations, and a formalized rule that judges should reject evidence obtained through torture.

In April, Zhao Chunguang, a national official overseeing police detention facilities, said there had not been a single case of torture to coerce a confession at any detention center in the past five years.

But Xinhua's report said Harbin Intermediate People's Court heard appeals Aug. 29 by four of the seven people who had been convicted by a trial court on torture charges.

Xinhua said the deceased man, identified by his surname, Liang, was detained by police on March 24 last year along with another man on suspicion of selling drugs. One of the police officers, Wu Yan, along with two people who weren't police officers, Pan Yongquan and Li Yingbin, gave him electric shocks and hit him in the face and head with a shoe, after which he died, it said.

In the only other case for which Xinhua provided details, a man surnamed Zhai was arrested on suspicion of selling drugs on March 7, 2013. Zhai testified that Cheng Xiaowei, Pan and Li Chunlong, another civilian, handcuffed him to an iron chair and tied wires from an old-fashioned telephone to his toes and started cranking the phone, giving him several rounds of electric shocks, Xinhua said.

Xinhua said that according to Chinese law, when suspects are being interrogated, torture is prohibited, at least two interrogators must be present and no non-police personnel are allowed. It said the Harbin cases "reflect the chaos in the process of law enforcement and severely hurts the public's trust in the judicial authority."

According to Chinese law, the maximum penalty for using torture to extract confessions is three years' imprisonment, rising to 10 years if severe or disabling injuries are caused, and a potential death penalty if death results.

Hong Daode, a criminal law professor at China University of Political Science and Law in Beijing, said, "It looks like the sentences given by the court are too lenient ... and it will set a bad example for future torture cases."

Any punishment remains rare.

Hong Kong-based Human Rights Watch researcher Maya Wang said police officers in China can commit torture with "impunity" because there are "no independent channels to make these complaints heard."

"Police officers who commit torture are rarely found accountable legally and even if they are ... the punishment given seems to be light compared to the crime committed," Wang said.