FBI investigates another police killing, this time of unarmed white teenager in Fresno, California

A third controversial police shooting in the United States in as many weeks is now being examined by federal authorities, officials report.

Dylan Noble, 19, was fatally shot by police in Fresno, California, as the teenager lay on the ground next to his pickup truck at a gas station.

Noble calls out "I'm shot" in a chilling cell-phone video taken by a bystander. He was reportedly struck by four police bullets.

One of the officers fired three rounds from his service handgun and a second officer fired one shotgun round, officials said.

The officers had responded to a call of a man in the area wearing camouflage clothing and carrying a rifle. They pursued Noble who was driving his pickup truck erratically until he stopped at the gas station.

Fresno Police Chief Jerry Dyer alleged that Noble at one point raised his shirt and reached for his waistband before he was shot. Officers believed he was about to draw a weapon, making the officers "afraid for their lives", said Dyer.

The shooting occurred in June, but controversy erupted after the video was released by the Fresno Bee.

The video which was taken after Noble had already been struck by two bullets, shows him lying on the ground on his back 25 June as two officers with their guns drawn stand just meters away from him. As officers yell: "Keep your hands up" and "show us you hands," a shot rings out. A third officer approaches and another shot is fired.

The officers were wearing body cameras, according to the police chief. The department will review the officers' actions to determine why they fired at Noble while he was on the ground and if there were other options, Dyer said.

"There is going to be questions," he told the Los Angeles Times. "It's an unfortunate tragedy."

"There was no firearm on this individual," Dyer told the Bee. "There was no firearm found in the pickup." Noble had no criminal history. The reported man in camouflage with a rifle was not located.

The FBI and the US attorney general's office will also investigate the shooting and will have access to all evidence, Dyer said.

News of the investigation comes in the wake of the controversial police shooting deaths this week of Alton Sterling in Baton Rouge, Louisiana, and Philando Castile in a Minneapolis suburb.

In the latest tragic twist four police officers have been shot dead and several others wounded apparently by a pair of snipers at a Black Lives Matter protest against the recent shootings in downtown Dallas, Texas.