Authorities this week rescued a 4-year-old boy who was found naked, beaten, severely malnourished and chained in a Mexico City apartment.

The boy, who could be a United States citizen, was rescued after an anonymous tipster notified child protection officials, the Daily Mail reports.

When authorities arrived at the apartment on Tuesday, the boy’s aunt and uncle initially denied that the boy was in the home. But police searching the apartment later discovered the boy tied up in a dark room.

The boy showed signs that he had been abused and tortured and was hospitalized for “multiple injuries,” according to the newspaper. Doctors discovered that the boy’s skin had been burned multiple times by cigarettes and that he also had been hit in the head repeatedly. He also suffered from malnutrition.

The boy had difficulty speaking, but he was able to say his own name — Antony — and the names of his parents.

The relatives told authorities they were just looking after the boy temporarily for his father.

Authorities are now caring for the child and helping him deal with the trauma he has endured.

One photograph from inside the apartment shows a silver chain tied around the boy’s thin legs; he appeared to be sitting or laying on top of a blanket on the floor.

An investigation into the boy’s detention started when Victor Hugo Lobo, a child protection official, received an anonymous letter with details about the boy.

Lobo has said those responsible for the boy’s captivity would be brought to justice.

It was not publicly known Saturday whether the boy’s father had been arrested.

It also was not immediately clear why authorities believed the boy may be a U.S. citizen, but the Mexico City prosecutor’s office has asked the U.S. Embassy for help in ascertaining the boy’s citizenship.

Feature photo: Police handout