The incident took place last evening, police said today, adding that the accused, who was the boy's maternal uncle, has been arrested.
The victim's parents left the child at his maternal uncle's house when they were going out for work,
"It was during this time that the youth sodomised the kid and threatened him of dire consequences if he spilled the beans," said a police official.
When they returned, the parents found their son crying. When they took him to a nearby hospital it was revealed that he was sexually assaulted as he was bleeding from his private part.