The United States is "done talking about North Korea" and China is aware it must act, U.S. Ambassador to the United Nations Nikki Haley said on Sunday after North Korea fired its second long-range missile this month and amid a push by Washington to impose stronger U.N. sanctions on Pyongyang.

"Done talking about North Korea. China is aware they must act. Japan and South Korea must increase pressure. Not only a U.S. problem. It will require an international solution," Haley posted on Twitter.

She then posted a link to photos of the United States, Japan and South Korea conducting bomber jet drills over the Korean Peninsula on Sunday. The United States flew two supersonic B-1B bombers as a show of force after Pyongyang fired an intercontinental ballistic missile (ICBM) on Friday.