Four US Marines killed in base accident

Four US Marines have been killed in what officials described as a tragic accident at a base in southern California.

They had been clearing unexploded ordnance at Camp Pendleton, near San Diego, a Marine official said.

The incident happened on Wednesday morning during a range maintenance operation. An investigation has been launched, a spokesman added.

No further details were released and the victims were not named.

In March, seven US Marines died in a training accident in Nevada.

Military investigators later ruled that human error had caused a mortar explosion during a night-time live-fire drill.