BEIJING (AP) — A foreign ministry official says China will "seriously" deal with any breaches of U.N. Security Council resolutions on North Korea should they be found.

However, ministry spokesman Geng Shuang said Saturday that Beijing "firmly opposes the U.S. imposing unilateral sanctions and 'long-arm jurisdiction' on Chinese entities or individuals."

China previously said it was "highly concerned" about a reported ship-to-ship transfer that could violate sanctions and it was investigating. The incident reported by Japan in the past week was the third reported transfer in the past month.

China has agreed to impose increasingly tough sanctions on North Korea over its nuclear weapons program, and Geng has said Beijing recently issued a statement explicitly banning ship-to-ship transfers.