A two-year old boy's decomposed body was found stuffed in a cooler box in a suspected abuse and murder case in Kedah.

Police made the shocking discovery at a Flat Paya Nahu unit in Sungai Petani early Thursday morning following a call about a domestic quarrel between the boy's 26-year-old mother and her 34-year-old boyfriend.

The toddler, believed to have died since November 9 from physical abuse, was found wrapped in a blanket in a cooler box, in one of the rooms in the flat.

Police also found the victim's four-year-old sister injured with bruises on her body.

Kuala Muda district police chief Assistant Commissioner Md Zukir Md Isa said the toddler's mother had told police about the body inside the cooler box.

Both the woman and her boyfriend were tested positive for drugs and have been detained for investigations.

The victim's sister was sent to Hospital Sultan Abdul Halim to undergo treatment.

Zukir said police are investigating the case under Section 302 and 325 of the Penal Code.