Police rescued a girl and a boy whose relatives kept the children gagged, bound and naked inside a water tank at their home, a Mexico City prosecutor said Thursday.

A photo published in Mexican newspapers Thursday shows a skinny, 6-year-old naked boy with his mouth gagged, his feet bound and his hands tied behind his back with strips of white fabric. The boy is seen sitting bent over in an empty, filthy tank.

The boy's 4-year-old sister was found the same way Tuesday night, prosecutor Miguel Angel Mancera said. He did not say how long the children were in the tank.

An anonymous caller reported hearing moans coming from the home, Mancera told MVS Radio.

Police detained an aunt, uncle and two others living at the home after rescuing the children. Mancera said authorities were investigating further before filing any charges.

The aunt and uncle — who started taking care of the children after their parents abandoned them — told authorities that's how they issued their punishments, Mancera said.

The children were being treated at a hospital for dehydration, hypothermia and unspecified wounds. Authorities found older injuries after examining the children, indicating they had suffered previous abuses, Mancera said.

The city was arranging for the children to undergo therapy, Mancera said.