"We'll see about North Korea," the US president told reporters after North Korea's ambassador to the United Nations said on Saturday that denuclearisation was off the negotiating table with the United States.

"I'd be surprised if North Korea acted hostilely," Trump said at the White House before leaving for Florida.

"He knows I have an election coming up. I don't think he wants to interfere with that, but we'll have to see ... I think he'd like to see something happen. The relationship is very good, but there is some hostility, there's no question about it."

The statement from North Korea comes as Pynongyang has demanded Washington offer new proposals to create a breakthrough in the stalled negotiations by the end of the year.

Experts in South Korea fear that North Korea will lift its self-imposed moratorium on nuclear testing and long-range missile testing if no progress is made before the deadline.

In a statement on Saturday Ambassador Kim Song said the "sustained and substantial dialogue" advanced by the United States is "none other than a time-saving trick to make expedient use of the DPRK-US dialogue solely in its domestic political agenda".

"We do not need to have lengthy talks with the US now and the denuclearisation is already gone out of the negotiating table," the ambassador added.

Ambassador Kim also blasted six EU member states on the UN Security Council that criticised recent short-range North Korean missile tests, calling them the "pet dog of the United States".

Earlier on Saturday US President Donald Trump spoke with South Korean President Moon Jae In by telephone, Moon's office said.

Both agreed that it was necessary to continue the dialogue with the Communist leadership in Pyongyang, during the 30-minute conversation, according to Moon's office.

"The momentum for dialogue should be maintained in order to achieve rapid results in the negotiations on denuclearisation," Moon's office said.

Denuclearisation refers to the nuclear disarmament of North Korea.

The tone between Washington and Pyongyang has deteriorated amid stalled talks.

North Korea's First Vice-Minister of Foreign Affairs Choe Son Hui on Thursday criticised Trump's recent statements alluding to the possible use of military force in the nuclear dispute and again describing North Korean leader Kim Jong Un as "rocket man."

Choe warned against a new war of words and called the repeated use of offensive language a "relapse of the dotage of a dotard."

US negotiations with North Korea have not progressed since their failed February summit in Vietnam.

Australian Associated Press