Monterrey - A pupil killed at least three people and injured five when he opened fire on his classmates at a high school in northern Mexico on Wednesday, officials said.The boy opened fire at Northeastern College in the city of Monterrey before trying unsuccessfully to kill himself, civil protection official Oscar Aboytes told AFP."A minor entered and fired at several of his companions," Aboytes said. "There are three dead and five injured."Mexico suffers regular gang violence but so far nothing appeared to indicate that the school shooting was gang-related."It is an unprecedented situation. Nothing like this has happened before" in schools in the surrounding state of Nuevo Leon, state security secretary Aldo Fasci told reporters.The deadly rampage came as the northeastern state of Quintana Roo, hundreds of miles from Monterrey, reeled from two shootings, thought to be linked to gangs or drug dealers, that left nine people dead.In 2014, 43 students from a teacher training college in southern Mexico went missing and are believed dead.