Image copyright Tokyo Electric Power Co Image caption Fukushima suffered a series of meltdowns after a huge earthquake and tsunami

Three former executives at a Japanese power giant have been formally charged with negligence over the 2011 disaster at the Fukushima nuclear plant.

The trio, formerly of Tokyo Electric Power Co (Tepco), will be the first to go to court over the incident.

A citizen's panel ruled last year they should face trial, forcing prosecutors to pursue the case.

The Fukushima Daiichi plant suffered a series of meltdowns following a massive earthquake and tsunami.

Among those charged is Tsunehisa Katsumata, who was Tepco chairman at the time of the disaster.

He and two other former executives have been charged with professional negligence. They have not been taken into custody.

Rare legal move

Prosecutors in Tokyo had twice decided against pressing charges, citing insufficient evidence.

But in a rare legal move, the panel's ruling forced a compulsory indictment of the three.

The panel said the three men did not take sufficient measures despite being warned of a risk of a tsunami near the Fukushima plant.

Japan's national broadcaster NHK said they planned to plead not guilty on the grounds they could not have anticipated the size of the tsunami.

One of the most powerful earthquakes ever recorded struck off the coast of Japan in March 2011, triggering a huge tsunami.

Almost 16,000 people died and more than 2,500 are still listed as missing.

None of the deaths, however, have been linked to the nuclear disaster, although there were a number of deaths in the subsequent evacuation.