A Japanese schoolboy is under investigation for allegedly dealing uranium online and for making explosives.

The 16-year-old is being investigated by the Metropolitan Police Department in Tokyo on suspicion of violating the Nuclear Reactor Regulation Law, the Asahi Shimbun reported.

He has also been accused of producing erythritol tetranitrate (ETN), which is used in explosives, in August 2018 in violation of the Explosives Control Law.

Police said the boy was being questioned on a voluntary basis, along with several other people who are thought to have bought radioactive materials from him.

They believe he may have refined and sold uranium out of an interest in science.

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The teenager came to the attention of authorities after the Nuclear Regulatory Agency discovered a substance advertised as “uranium 99.9 per cent” was being sold on a Yahoo online auction site.

In January 2018, the agency reported its findings to the Metropolitan Police Department, which tracked the transaction to the seller and several others, including the student, who had bought the substance.

Police confirmed it was uranium and searched the student’s home, where they also seized yellowcake, a type of uranium concentrate, the Japan Times reported.

The boy is suspected of manufacturing the substance from uranium ore and putting it up for sale online.

Several others who allegedly bought yellow cake from the boy are also under investigation.

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One security analyst has argued the boy was probably not a terrorist but actually a “chemistry geek”.

“This is not a case of terrorism, even of the home-grown variety,” Lance Gatling, founder of Tokyo-based Gatling Associates, told Japan’s Kyodo news agency.

“To be honest, you would simply not believe what chemistry geeks will do ... [There are] probably a few dozen guys who have tried to fabricate sarin gas in their bathrooms.”