China has banned exports to North Korea of a range of technologies that could be used to build weapons, the latest move to deter Pyongyang's internationally condemned nuclear programme.Prohibited goods include ring magnets, high strength aluminium alloys, laser welding equipment, and an array of compounds that can be used to produce nuclear and chemical weapons, the Ministry of Commerce said in a statement late Tuesday listing restricted "dual use" items.China is North Korea's largest trading partner and has been its key diplomatic protector for decades. But relations have soured over the North's nuclear tests and long-range missile launches, with Beijing supporting UN sanctions in a security council vote in March.The ban comes in the wake of UN resolution 2270, which aims to prevent the production of nuclear weapons and imposed fresh sanctions on the pariah state after Pyongyang's nuclear test at the start of the year.Chinese President Xi Jinping met with a visiting North Korean official earlier this month and stressed the importance of keeping "friendly relations" between the countries. The envoy reportedly told Chinese officials Pyongyang would continue its nuclear programme.North Korean leader Kim Jong-Un has not visited China since coming to power and his Chinese counterpart Xi Jinping has not been to Pyongyang.North Korea held its first party congress for nearly 40 years in early May, formally endorsing leader Kim Jong-Un's policy of expanding the country's nuclear arsenal.