UNITED NATIONS, Oct 4 (Reuters) - The United States asked the U.N. Security Council to meet on North Korea on Wednesday after Pyongyang fired a ballistic missile over Japan, but diplomats said China and Russia are opposed to a public discussion by the 15-member body.Nuclear-armed North Korea test-fired a ballistic missile farther than ever before on Tuesday, sending it soaring over Japan for the first time in five years and prompting a warning for residents there to take cover."We must limit the DPRK's ability to advance its unlawful ballistic missile and weapons of mass destruction programs," U.S.However, China and Russia told council counterparts they are opposed to a public meeting, arguing that the reaction of the council should be conducive to easing the situation on the Korean Peninsula, diplomats said.In recent years, veto powers China and Russia have suggested U.N. sanctions on North Korea be eased for humanitarian purposes and to entice Pyongyang back to stalled international talks aimed at persuading leader Kim Jong Un to denuclearize."