'Rookie cop fired on 12yo from 3 metres'

The police officer who shot dead a 12-year-old boy in Cleveland, Ohio, was about three metres away when he fired, police officers say.

The boy, Tamir Rice, was shot on Saturday and died on Sunday after undergoing surgery.

Police said two officers arrived at the scene at a recreation centre after receiving a 911 call that someone at the park was carrying a "probably fake" gun and pointing it at people.

The first-year officer fired two shots after he saw Rice pull what he thought was a gun from the waistband of his pants, Cleveland police said at the press conference on Monday.

In response to the incident, the international activist group Anonymous, hacked the city of Cleveland's website.

Anonymous is upset that the Cleveland Police Department will not release the name of the "rookie officer" that shot Rice, and said the officer should have tasered Rice instead.

"Shooting him in cold blood was not necessary with these non-lethal options available," a member said in the YouTube video.

Toy guns are supposed to have orange tips to show that they are not real. Rice's gun did not.

The two officers involved in the incident have been placed on administrative leave, officials said.

The shooting of Rice, who is black, happened at a sensitive time as the nation anxiously awaited to hear a grand jury verdict on the fatal shooting of unarmed black Michael Brown by white police officer Darren Wilson in Ferguson, Missouri.

A grand jury will also be convened in the Cleveland case. Cuyahoga County Prosecutor Tim McGinty said that evidence will be presented to the jury, which will decide whether to bring criminal charges against the police officer.

WKYC reported that Rice's family is planning their own investigation into the incident.

"We are going to conduct our own investigation," said Rice family lawyer Tim Kucharski. "We are going to talk to witnesses. We will get all the 911 tapes, the radio dispatch records as to what was said to the police, what the officers knew."