The Japanese government aims to decide around September on the method for extracting fuel debris from the No. 3 reactor of the crisis-hit Fukushima nuclear complex following a recent survey using a robot, industry minister said Tuesday.

"Valuable information has been obtained from a survey inside the reactor using a submersible robot," Economy, Trade and Industry Minister Hiroshige Seko told reporters.

The undersea robot for the first time captured images of materials, deemed "highly likely" to be melted fuel, scattered in the crippled reactor during the survey conducted last week.

The investigation was launched as the government and the operator Tokyo Electric Power Company Holdings Inc. aim to scrap the Nos. 1 to 3 reactors at the Fukushima Daiichi complex after they suffered core meltdowns following the massive earthquake and tsunami in 2011 that triggered the world's worst nuclear disaster since the 1986 Chernobyl crisis.

Under the road map for decommissioning, they aim to finalize the extraction method by the first half of fiscal 2018 and start work in 2021 to remove the fuel debris.

The process is one of the most difficult stages of the decommissioning project, which is expected to take at least 30 to 40 years to complete. Critics question whether the process will move forward as scheduled as radiation levels in the reactors still remain extremely high.

"At the current stage, we will proceed with the decommissioning in line with the road map," Seko said, noting the need to evaluate the feasibility at the same time.

The survey showed what is likely to be melted fuel attached to control rod devices extending from the bottom of the reactor pressure vessel in an indication the fuel melted through.

A build-up of deposits on the bottom of the primary containment vessel was also found up to a height of at least 1 meter, according to the operator.