Beijing: A "deeply concerned" China on Monday asked Japan to return to the US over 300 kg of weapons-grade plutonium, which could arm upto 50 nuclear bombs, the latest in a series of disputes between the two distrustful neighbours.
"Japan`s large stock of nuclear material, including weapons grade nuclear substances, involves nuclear security and non-proliferation risks," Chinese Foreign Ministry spokeswoman Hua Chunying told a press briefing here.
"Japan has avoided returning the material which caused international concern. China is deeply concerned and is expecting an explanation," Hua said.
Her comments weeks after America demanded return of the atomic material it gave to Japan during the Cold War.
It is against the regulations of the UN nuclear watchdog, the International Atomic Energy Agency, which require countries to keep a balance between the demand and supply of nuclear materials, Hua said.
The US offered 331 kg of weapons grade plutonium, partly produced by Britain, to Japan during the Cold War, Japan`s Kyodo news agency reported.
The highly concentrated plutonium, which is kept by Japan`s atomic energy agency could be used to produce 40 to 50 nuclear weapons. Japan holds another 44 tonnes of plutonium which could be used for nuclear reactors, China`s state-run Xinhua news agency reported.
Hua urged Japan, a member of the Treaty on the Non- proliferation of Nuclear Weapons, to honour its obligations and return the material at an early date.
"We also urge Japan to settle the imbalance between its need for and supply of nuclear materials in accordance with IAEA requirements," Hua said.
China is locked in a bitter territorial dispute with Japan in the East China Sea and expressed concern that Tokyo is trying to strengthen its arsenal.