Diplomats say North Korea is suspected of shipping ballistic missile components to a Syrian company, in apparent violation of U.N. sanctions against Pyongyang.

U.N. diplomats say South Korean authorities seized at least 445 graphite cylinders in May from a Chinese ship in the South Korean port city of Busan. The cylinders, which were disguised as lead pipes, were headed for a Syrian company with North Korean links.

The diplomats said China has promised to investigate the apparent sanction violation, which was reported last month to the U.N. Security Council North Korea sanctions committee.

North Korea is banned from importing or exporting nuclear and missile technology under international sanctions put in place after it conducted nuclear tests in 2006 and 2009.

Syria is also under U.S. and European arms sanctions. But there is no U.N. weapons embargo against the government of President Bashar al-Assad, who is engaged in a 20-month conflict with opposition groups.