A senior US diplomat has urged North Korea to return to the negotiating table immediately to complete stalled nuclear talks.
The US special representative for North Korea, Stephen Biegun, added that Washington would not accept an end of year deadline set by Pyongyang to make concessions in the negotiations.
The US had originally strived for North Korea's denuclearisation in return for sanction relief, before failed talks earlier this year, with North Korean leader Kim Jong Un rejecting the stance.
Speaking in Seoul, during talks with South Korean officials, Mr Biegun said the United States "does not have a deadline", adding it is "fully aware of the strong potential for North Korea to conduct a major provocation in the days ahead".
Such action would be unhelpful, he said, in securing lasting peace in the Korean Penninsula.
The US diplomat added: "Let me speak directly to our counterparts in North Korea: It is time for us to do our jobs.
"Let's get this done. We are here. And you know how to reach us."
Senior North Korean officials have recently said denuclearisation is already off the negotiating table, threatening to lift a self-imposed moratorium on nuclear and long-range missile tests.
A failed second summit with US President Donald Trump in February saw a breakdown in progress between the two nations, although the American leader did make an unprecedented visit to North Korea in June.
In recent months, a spate of projectile test-launches from North Korea has prompted international condemnation, the UK among those nations calling for new sanctions on the country.
Experts say North Korea could launch a satellite-carrying rocket or an intercontinental ballistic missile if the US fails to meet its deadline, after fears of development in the country's long-range capability.
North Korea's military chief, Pak Jong Chon, asserted that the North has built up "tremendous power" and that the findings from the recent tests would be used to develop new weapons to allow the country to "definitely and reliably" counter US nuclear threats.
Mr Biegun called the latest North Korean statements "so hostile and negative and so unnecessary", adding that they do not reflect the spirit and content of past discussions.