A 7-year-old girl was killed in a Bronx fire early this morning that also injured her younger sister, and officials have characterized the blaze as suspicious.

Hazel Martinez, 7, and her 3-year-old sister Hayley were reportedly two of four children in their family's fourth-floor apartment on Grant Ave near East 64th Street at around 3:15 a.m. this morning, when the blaze broke out. Firefighters pulled both girls out of the building and tried to resuscitate them, but Hazel was pronounced dead at a nearby hospital. ""One of the girls passed away, it’s very difficult right now," a neighbor told the Daily News. "There were four children in the apartment, they have them here on oxygen."

Investigators say they found a five-gallon gasoline container at the scene, and they also believe someone tampered with the natural gas line. The incident is still under investigation; the family says they do not know how the fire started. "It was heart-breaking—they lost a child so young," building resident Nicole Salem told the Post. "The firefighters tried their best." Hayley is listed in critical condition at Lincoln Hospital, where an adult building resident is recuperating as well.