The United States is "done talking about North Korea" and China must decide if it is willing to back imposing stronger United Nations sanctions on North Korea over its two long-range missile tests this month, the US Ambassador to the United Nations, Nikki Haley, has said.
In a statement, Ms Haley said that any new UN Security Council resolution "that does not significantly increase the international pressure on North Korea is of no value".
The United States flew two supersonic B-1B bombers as a show of force after Pyongyang fired a second intercontinental ballistic missile (ICBM) on Friday.
"China must decide whether it is finally willing to take this vital step. The time for talk is over," she said.
The Chinese mission to the United Nations did not immediately respond to a request for comment.
The United States has been in talks with North Korean ally China on a draft UN Security Council resolution to impose stronger sanctions on North Korea. Ms Haley gave China a draft text after North Korea's July 4 ICBM test.
Ms Haley said last Tuesday that the United States had been making progress with China.
Some diplomats had expected the United States, Japan and South Korea to ask for the 15-member UN Security Council to meet on Monday over the test. However Ms Haley said that the United States saw "no point in having an emergency session if it produces nothing of consequence".
Such a meeting would have set the stage for a likely showdown between the United States and Russia over whether Friday's launch was a long-range rocket test. It was unclear if any other Security Council members, such as Japan, planned to request a meeting.
Diplomats say China and Russia only view a long-range missile test or nuclear weapon test as a trigger for further possible UN Security Council sanctions.
The Pentagon and South Korean military believe Friday's test was an ICBM. However, a Russian Defense Ministry official said Moscow's data indicated it was only a medium-range missile.
The United States and Russia have waged rival campaigns at the Security Council over the type of ballistic missile fired by North Korea on July 4. Western powers said it was an ICBM, while Russia said it was medium-range.
North Korea has been under UN sanctions since 2006 over its ballistic missile and nuclear programmes and the Security Council has ratcheted up the measures in response to five nuclear weapons tests and two long-range missile launches.
Ms Haley has said some options to strengthen UN sanctions were to restrict the flow of oil to North Korea's military and weapons programmes, increasing air and maritime restrictions and imposing sanctions on senior officials.
Traditionally, the United States and China have negotiated sanctions on North Korea before formally involving other Security Council members.
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