Two British ships have arrived in eastern Japan to transport a shipment of plutonium — enough to make dozens of atomic bombs — to the U.S. for storage under a bilateral agreement.

Kyodo News agency said the two ships arrived up early Monday on the coast of Tokai village, northeast of Tokyo, home to the country's main nuclear research facility, the Japan Atomic and Energy Agency. It will take several hours to load the plutonium onto the ships.

The British-flagged ships operated by Pacific Nuclear Transport Ltd. will take the 331 kilograms (730 pounds) of plutonium to a U.S. government facility in South Carolina.

Japan's massive stockpile and its fuel-reprocessing ambitions for power generation have been a source of international security concerns.