The US is closely monitoring North Korea for a threatened “Christmas gift” missile launch or nuclear test.
The move would end Pyongyang’s self-imposed weapons test moratorium and heighten tensions in the region.
It would also deal a major blow to one of Donald Trump’s key foreign policy goals, which aimed to draw North Korea into talks on scrapping its nuclear arsenal.
Earlier this month, the authoritarian regime conducted what the US said was an engine test.
Officials fear it could signal the possible launch of an intercontinental ballistic missile (ICBM) in the coming days or weeks.
North Korean leader Kim Jong Un had given the US until the end of the year to propose fresh concessions in talks over his nation’s nuclear weapons.
Pyongyang said in early December that it was up to Washington to decide what “Christmas gift” it will receive.
Donald Trump’s historic summits with Mr Kim over the past two years have failed to make a breakthrough.
Despite a joint commitment “to work toward complete denuclearisation of the Korean Peninsula”, negotiations stalled after the US rejected North Korean demands for broad sanctions relief in exchange for a partial surrender of its nuclear capabilities.
Victor Cha, a Korea expert at the Centre for Strategic and International Studies, said a review of the possible launch sites in North Korea shows that they are a “basically ready to go”.
He said the expected launch could be a test of a sea-based ballistic missile or a solid-fuel rocket, which would give the US or others less warning and time to prepare.
US Defence Secretary Mark Esper said earlier this week he was aware of the talk about a possible test.
“I’ve been watching the Korean Peninsula for a quarter-century now. I’m familiar with their tactics, with their bluster,” he said.
“We need to get serious and sit down and have discussions about a political agreement that denuclearises the peninsula. That is the best way forward and arguably the only way forward if we’re going to do something constructive.”
Deputy Secretary of State Stephen Biegun, the special US envoy for North Korea, said: “We are fully aware of the strong potential for North Korea to conduct a major provocation in the days ahead.
“To say the least, such an action will be most unhelpful in achieving lasting peace on the Korean Peninsula.”
Anthony Wier, a former State Department official who tracks nuclear disarmament for the Friends Committee on National Legislation, said: “North Korea has been advancing. It has been building new capabilities.
“As long as that continues, they gain new capabilities to try new missiles to threaten us and our allies in new ways.”