A grand jury in the US state of Ohio declined to bring criminal charges against Cleveland police officers involved in the fatal shooting last year of a 12-year-old boy, a prosecutor said on Monday.

The death in November 2014 of Tamir Rice - a black child who had been carrying a replica gun in a playground when he was shot dead - and the fatal shootings of other African-Americans by police have triggered protests across the United States.

Surveillance video showed Rice was fatally shot within seconds of the patrol car arriving at the scene as he began to pull the toy gun out of his waistband. The boy died hours later in a hospital.