With tension rising over North Korea's nuclear and ballistic missile tests, US Secretary of State Rex Tillerson said in September that Washington was "probing" to see if Pyongyang was interested in talks on its denuclearization.

Trump later called him out for "wasting his time" trying to talk to the North Korean leader, Kim Jong-un.

But the president struck a softer tone in Seoul Tuesday, saying he believes the North should "make a deal" on its weapons program for its people and all of humanity. He also said he sees "certain movement," but did not elaborate.

The president made clear, according to the official, that North Korea should first reduce the threats, end provocations and move towards sincere steps to ultimately denuclearize.

"And I think that North Korea has shown that, really, they are the ones that are putting forward preconditions," he said. "They are the ones who have been saying they're unwilling to talk about nuclear weapons; that that's not on the table. That's a nonstarter for us."

In China, Trump plans to enlist Beijing's commitment to enforcing sanctions against Pyongyang.

"I think that if you look at the activity across that border, certainly there is still some trade taking place," the official said. "There is still some financial links that exist that should not under (UN Security Council) resolutions."

China is North Korea's only major ally and is responsible for about 90 percent of its external trade.

"China is doing much more than it's ever done in the past," the official noted. "But it's not the time for complacency or for allowing people to slip through loopholes and for a lot of that residual activity to continue.

"We know that some of that activity is continuing, and we're going to work closely with the Chinese to identify that activity and end it," he said. (Yonhap)