An autopsy into the death of a young child in La Plata, Maryland, whose remains were discovered as his mother pushed him on a park swing, has returned inconclusive.

The examination did not reveal the cause or manner of the death of the 3-year-old, Charles County Sherriff spokeswoman Diane Richardson told the Associated Press.

Officials will now carry out further investigations, including a toxicology test, added Ms Richardson.

Detectives are also attempting to establish what happened in the days leading up to the child’s death.

The child’s 24-year-old mother, who has not yet been identified, has spent a third day in hospital after she was found pushing the boy on the swing at 7am on Friday morning.

It is believed she was pushing her son for hours before police arrived on the scene, after the force received a call from a witness who said the pair had been at the swing for an unusual amount of time.

Other witnesses told the police they saw the mother and child at the park the previous day. Police will now try to determine whether the mother left the park in that time.

Police previously said there were no obvious signs of foul play but that it hadn't been ruled out.

Sheriff's spokeswoman Diane Richardson said at the time: “We have a lot of work to do to try to figure out what happened to this child.

“At about 7 am we received a call in reference to a woman pushing a toddler in a swing for an unusual period of time. The caller said the woman had possibly been in the park since yesterday.