A 51-year-old Indian-origin drug offender was sentenced to three years in prison on Monday for punching a prison officer in 2022 and causing a fracture on his face, a media report said.

Kaliappan Kumarasamy, who was undergoing treatment at a drug rehabilitation centre located within Changi Prison, pleaded guilty to voluntarily causing grievous hurt to chief warder Lim See Chuan, 41.

Kaliappan told the investigators that he did so as he was feeling angry because of an internal investigation against him over an unrelated dispute, The Straits Times newspaper reported.

The court heard that in December 2022, Lim was escorting Kaliappan back to his cell, and the pair started talking as they walked down a corridor.

"While they were talking, the victim touched the accused’s right upper arm as a friendly gesture. However, a moment later as they continued walking, the accused suddenly punched the victim’s face forcefully with his left fist," Deputy Public Prosecutor James Chew told the court.

"The victim fell to the ground. As the victim was picking himself up, the accused stood in front of him and threw another punch at the victim’s head with his left fist. This punch missed the victim’s head," The Times quoted Chew as saying. Lim, who was bleeding from his nose and mouth, activated his communication device for assistance, prompting his colleagues to rush over.

The report said that an officer had to use pepper spray on Kaliappan as he continued to attack Lim. Lim, who was taken to Changi General Hospital, continued to suffer from facial numbness, Chew told the judge as he asked for more than a three-year jail-term for Kaliappan.

"The accused had brazenly assaulted the victim despite being completely unprovoked. He had done so because he was angry at (the Singapore Prison Service) for a separate investigation against him. Such ‘revenge’ attacks... simply cannot be allowed or tolerated," Chew said in the court.

For voluntarily causing grievous hurt to a public servant, an offender can be jailed for up to 15 years and fined or caned. According to Singapore law, Kaliappan cannot be caned as he is over 50 years-old.