"The primary reason for the death seems to be suffocation. However, what caused the suffocation is not known and we have sought help from forensic experts," Karaya police station chief S.R. Bhattacharya said.

"So far, we have not found anything to suggest that there was any foul play or they (the parents) attempted suicide. The investigation is on," he added.

The neighbours called the police early Monday after they grew suspicious when nobody in the house responded to their repeated knocks.

"When we broke open the door we found all the three lying motionless on the bed. While the baby was declared dead, her parents were admitted to hospital," Bhattacharya said.