South Korean President Moon Jae-in on Monday urged the United States (US) to “lower the threshold for talks” with the North as his aides held rare talks with a Pyongyang general on ways to defuse tensions.

Moon has sought to use the Pyeongchang Winter Olympics, that ended on Sunday, to open dialogue between Washington and Pyongyang in the hopes of easing a nuclear standoff that has sparked global security fears.

Pyongyang mounted a charm offensive during the Games, sending athletes, cheerleaders and performers.

The North's leader Kim Jong Un also sent his sister to attend the opening ceremony before dispatching Kim Yong Chol, a powerful general in charge of inter-Korea affairs for the ruling Workers' Party, to Sunday's closing event.

But there was no known interaction between the North and the US during the Games and Washington on Friday imposed what US President Donald Trump described as the “heaviest ever” sanctions on the Kim regime.

“I think the US needs to lower the threshold for talks and the North also needs to show determination for denuclearisation,” Moon said in a meeting with Liu Yandong, a Chinese envoy to the closing ceremony.

“It's important that the US and the North sit together as soon as possible,” Moon said, urging efforts by Beijing to make that happen.

Moon, in a meeting with Kim Yong Chol on Sunday, also urged the North to open dialogue with the US as soon as possible, to which Kim responded by saying the North was “very willing” to hold talks.

But the US has ruled out any possibility of talks before the North, which since last year has staged multiple missile and nuclear tests, makes steps towards denuclearisation.

“We will see if Pyongyang's message today, that it is willing to hold talks, represents the first steps along the path to denuclearisation,” the White House said in a statement.

“The maximum pressure campaign must continue until North Korea denuclearises,” it said.

Kim Yong Chol also met with Moon's top advisers including national security adviser Chung Eui Yong on Monday as conservative demonstrators denounced his presence in the South.

Kim is accused of masterminding deadly attacks on the South, including the 2010 sinking of a South Korean warship that left 46 dead. Seoul accused Pyongyang of torpedoing the ship, a charge the North denies.

Dozens of conservative activists held a protest near a luxury Seoul hotel where Kim and seven other North Korean delegates are staying, ripping off the general's portrait and torching the North's national flags.

Hundreds of conservative Seoul lawmakers and their supporters also held a separate protest in Seoul, waving banners including “Arrest Kim Yong Chol! “