TOKYO (AFP) - A robot arm has successfully picked up pebble-sized pieces of radioactive fuel at Japan's Fukushima nuclear plant in a complex operation seen as key to cleanup efforts after the 2011 meltdown, officials said on Thursday (Feb 14).

Operator Tokyo Electric Power (Tepco) on Wednesday sent down a remote-controlled probe to the melted fuel at the bottom of the plant's reactor 2, one of three that melted down after a massive earthquake and tsunami in March 2011.

It caught five small pieces of the fuel debris and lifted them up about 5cm.

"We were able to confirm that the fuel debris can be moved," said Yuka Matsubara, a spokesman.

"We accomplished the objective of this test," she told AFP, adding that the company plans to actually remove some fuel debris as a sample by March next year.

Robots have already peered inside the reactor to allow experts to assess the melted fuel visually, but Wednesday's test was the first attempt to work out how fragile the highly radioactive material is.

Removing the melted fuel is considered the most difficult part of the massive cleanup operation in the wake of the worst nuclear disaster since Chernobyl.

It is not expected to begin until 2021, and Tepco has other issues to resolve including how to dispose of large quantities of contaminated water stored in containers at the plant site.

The March 2011 tsunami that caused the meltdown was triggered by a massive undersea quake and killed around 18,000 people.

Tens of thousands were forced to evacuate their homes because of the threat of radiation.

The authorities have been working to rebuild the region, about 240km north of Tokyo, although areas near the crippled plant remain uninhabitable because of radiation dangers.