Japan has confirmed that officials intercepted North Korean cargo last year containing military-grade aluminum alloy bars, which can be used to make parts for missiles.

Chief Cabinet Secretary Yoshihide Suga, the government’s top spokesman, said the cargo was found in late August aboard a Singapore-registered cargo ship at Tokyo Port. The vessel had called at Dalian, China, after setting off from North Korea and was bound for Myanmar, the Asahi Shimbun reports.

Officers from Tokyo Customs identified the contents as high-grade aluminum alloy, commonly used in building centrifuges for uranium enrichment.

North Korea is subject to a United Nations-backed embargo on its imports and exports of nuclear weapons and other objects for its production.

The United Nations slapped tough new sanctions on the regime over its defiant nuclear test in December. Pyongyang renewed threats of a “pre-emptive nuclear strike” in response to the US’ “hostile policy” and vowed to scrap an armistice with South Korea as tensions run high in the Korean peninsula.