A 3-year-old boy was killed and his 7-year-old sister was injured after being hit by gunfire while at a family gathering in Buffalo, New York, officials said.
Police who responded to the Friday night incident rushed the boy to the hospital, where he was pronounced dead.
His sister suffered graze wounds but is expected to recover, according to police.
"Last night was a very tragic night for our community," Buffalo Police Commissioner Joseph A. Gramaglia said during a press conference Saturday.
Gramaglia said the shooting had not been related to the family gathering.
"It was a hot night with a lot of people out, and the gunfire was unrelated to the gathering," he said. "These children were simply out enjoying a summer evening when tragedy struck."
"A 3-year-old riding his tricycle, having fun with members of his family on a hot summer night, his 7-year-old big sister right by his side, and out of nowhere gunfire erupts. And the children are struck by gunfire," Buffalo Mayor Byron Brown said.
Gramaglia commended the speed with which officers responded to the shooting, saying they arrived on the scene "very quickly."
According to Erie County District Attorney Michael Keane, the mother of the two children is a well-known member of the community who is active in Most Valuable Parents, a local organization focused on improving safety in Buffalo.
"She is a strong woman, consistently working with other families to keep our children safe," he said. "And now this tragedy has struck her own family."
Police have not said whether any person or persons of interest have been identified as of Sunday afternoon, and they are encouraging anyone with information about the shooting to come forward.
A gun recovered at the scene is currently undergoing testing, police said.
"We need the community to come together and help us put an end to this violence," Gramaglia said. "Our hearts are with the family of these children, and we will do everything in our power to bring justice for this senseless act."