"We are willing to talk, but not until we see a total stop of the nuclear process and of any test there," the US envoy, Nikki Haley, told reporters ahead of a closed-door Security Council meeting.
Washington and Beijing -- the North's sole diplomatic and military ally -- are working on a new Council resolution targeting Pyongyang, she added.
"That's what we are working on now. We don't have it done yet," she said.
"Absolutely, sanctions is something that we are looking at and we are going to continue to see where that takes us."
On Sunday, North Korea launched what appeared to be the longest-range missile it has ever successfully tested, sparking global alarm.
The missile, launched on an unusually high trajectory, flew to an altitude of 2,111.5 kilometers (1,312 miles) and travelled 787 kilometers before landing in the Sea of Japan (East Sea).
That suggests a range of 4,500 kilometers (2,800 miles) or more if flown for maximum distance, analysts said.
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