A three-year-old boy has shot dead his one-year-old brother after picking up a gun at their Cleveland home, officials said.

Police are investigating who brought the weapon into the house, and charges could be brought against that person, police said.

"A three-year-old cannot be held accountable for a tragedy like this," Cleveland police chief Calvin Williams said.

He said that someone had to have supplied the weapon or "knew the weapons were there and didn't do anything to safeguard them, so people will be held accountable for this tragedy".

The older child picked up the unattended gun and shot the younger one in the head, police said.

The victim, identified as Braylon Robinson, was taken to hospital and later pronounced dead.

"It's a sad day for Cleveland," Mr Williams told reporters outside the home.

"This fascination that we have with handguns, not just in this city but in this country, has to stop.

"This is a senseless loss of life."

Neighbours said the mother lived in the house with at least three small children.