The US is "very active" persuading North Korea to resume talks when the year-end deadline set by Pyongyang is near, according to a South Korean official.

Speaking at a press conference, South Korean national security adviser Chung Eui-yong said today that the United States is working hard to bring North Korea back to its discussions on denuclearization, and that Seoul is also important. "serious" mindset due to the deadline imposed by Pyongyang with Washington.

North Korean leader Kim Jong-un in April gave the US a deadline until the end of this year to show a more flexible approach to the issue of denuclearization. North Korean officials warned the United States not to ignore this deadline.

A senior North Korean diplomat said on November 8 that the door to opportunities for talks with the United States was closed and added that Pyongyang wants the United States to make more positive actions before the end of this year.

South Korea has set up a series of plans in anticipation of the deadline being exceeded but the US and North Korea have not achieved any positive results, Chung said, but did not disclose further details.

"Only when high-level talks between the two countries are held and lead to significant progress will the third US-North Korea summit be likely to take place," he said.

US President Donald Trump and North Korean leader Kim Jong-un in June agreed to resume the denuclearization talks that were delayed after the second US-North Korea summit in Vietnam in February.

Last month, however, US-North Korean officials first met in Stockholm, Sweden, but the talks failed when the North Korean delegation said the US did not show flexibility. North Korea still wants the US to lift sanctions as a premise for negotiations, but Washington has demanded that Pyongyang must give up its nuclear program first.