Police have registered an FIR against a 34-year-old man in Mumbai for allegedly molesting his minor niece and threatening to kill her younger brother when she resisted his assault and tried to raise an alarm, an official said on Wednesday.

According to the official, the accused molested his 13-year-old niece when her parents were away for some work and her 10-year-old brother was playing outside their residence. The family resides in a shanty in suburban Goregaon (East), he said.