Tensions are quickly rising between the United States and North Korea, which has ramped up pressure as it demands concessions by President Donald Trump's administration by the end of the year.
The United States called a UN Security Council meeting for Wednesday on North Korea's series of rocket launches, the latest return to antagonism as diplomacy languishes.
Monday's announcement came two days after North Korea claimed to have carried out a "very important" but otherwise unspecified test, in a hint that it may have further actions in store.
Trump has met three times with North Korean leader Kim Jong Un to discuss Pyongyang's nuclear program, describing him a friend and hailing the comparative calm achieved since 2017 when fears were growing of all-out war.
But North Korea is seeking a comprehensive deal that includes sanctions relief, especially with Trump heading next year into a potentially difficult re-election fight.
- Insults back -
Trump said Saturday that Kim has "too much to lose, everything actually, if he acts in a hostile way" and said he would be "surprised if North Korea acted hostiley."
In a rare personal attack on Trump since the start of diplomacy, Kim Yong Chol, a longtime aide to the top leader, called the US president a "heedless and erratic old man" and condemned his "odd words and expression."
If Trump is not "astonished" by North Korea's response, "we will be irritated," Kim said in a statement quoted by the official Korean Central News Agency.
The United States, which holds this month's presidency of the Security Council, called Wednesday's meeting to give a "comprehensive update" on the Korean peninsula and postponed a session on the authoritarian state's human rights record, a State Department spokesperson said.
The meeting will look at "recent missile launches and the possibility of an escalatory DPRK provocation," the spokesperson said, referring to the North by its official name, the Democratic People's Republic of Korea.
The Security Council also met last week behind closed doors at the best of European nations to condemn 13 missile tests by North Korea.
- North Korea 'in a box' -
Frank Aum, a senior expert on North Korea at the US Institute of Peace, said Pyongyang is raising the temperature as it believes the United States is in no rush to make a deal.
"I think they have decided, we don't want to play the US game, where the US gets all the benefits of reduced military tensions and North Korea gets no benefits," said Aum, who formerly advised the US defense secretary about the authoritarian state.
But the North Koreans have "put themselves in a box" and could alienate China, their main diplomatic ally and aid provider, if they take major action such as a new nuclear test or a long-range ballistic missile test, Aum said.
"They have to respond to the end-of-year deadline passing, otherwise it looks pretty stupid, but at the same time they can't respond too robustly, otherwise they will get a hard response back from the US and also China," Aum said.
He said the United States and North Korea could work out an interim deal which does not satisfy either side but serves as a base and avoids a flare-up.
Vipin Narang, a political scientist at the Massachusetts Institute of Technology who closely watches North Korea, said Kim likely felt humiliated by February's summit with Trump in Hanoi.
The meeting ended in stalemate, with Trump's aides encouraging him to wait for tangible signs that North Korea is giving up its nuclear arsenal.
Kim's "own hardliners at home probably gave him some sort of deadline to get some sanctions relief from the US," Narang said.
North Korea and the United States resumed working-level talks in October in Stockholm, but the North Korean delegation pronounced the meeting a failure.
"There's a risk of going back to 2017's tensions, or even worse, because there are very few diplomatic off-ramps left," Narang said.
"If you've already tried, essentially, the diplomatic nuclear option with a presidential summit, it would be very difficult for North Korea to go back to a working-level process," he said.
US President Donald Trump has met three times with North Korean leader Kim Jong Un to discuss Pyongyang's nuclear program
US President Donald Trump, pictured (left) with North Korea's Kim Jong Un at the Military Demarcation Line dividing North and South Korea, said he would be "surprised" by hostility from Pyongyang
South Koreans watch footage of a North Korean missile launch shown at a railway station in Seoul in October 2019