"You should act quickly, get the deal done," Trump tweeted Sunday, referring to North Korean leader Kim Jong Un. "See you soon!"

Kim and Trump have met three times since June last year, but talks have been gridlocked since their Hanoi summit in February broke up in disagreement over sanctions relief, while October's working-level talks rapidly broke down in Sweden.

Pyongyang has set Washington a deadline of the end of the year to come forward with a fresh offer, and foreign ministry advisor Kim Kye Gwan said the US was "buying time while acting as if it has achieved progress".

He interpreted Trump's tweet as a "signal" for a new summit, he said in a statement carried by state news agency KCNA, but declared: "We are not interested in such useless talks any more."

"We will not give anything to the US president to brag about when we have received nothing in return," he went on, adding the North should be "rewarded for what President Trump touts as his achievements".

The implied criticism of Trump by name is a departure for Pyongyang, which has long limited its frustration to other administration officials.

Last month, adviser Kim declared: "Contrary to the political judgment and intention of President Trump, Washington political circles and DPRK policy makers of the US administration are hostile to the DPRK for no reason," using the initials of North Korea's official name.

In September he was fulsome in his praise for the US leader, saying that Trump was "different from his predecessors" and that he placed his hopes in "President Trump's wise option and bold decision".

But as the North's deadline approaches it has issued a series of increasingly assertive statements -- while also carrying out a number of weapons launches.

Washington should withdraw its "hostile policy" if it wants dialogue to continue, Kim said Monday, without elaborating further.

Trump's tweet came after Washington and Seoul agreed to postpone annual joint aerial exercises to create space for diplomacy with Pyongyang, which condemns such drills as preparations for invasion.