However, the North Korean leader has chosen to spend his birthday with Chinese president Xi Jinping, Mr Trump's greatest geopolitical opponent.
The latest trip comes after United States and North Korean officials are believed to have met in Vietnam to discuss the location of a second summit between Kim and Trump following their first meeting in Singapore in June previous year.
North Korean leader Kim Jong Un arrived in China Tuesday to meet with Chinese President Xi Jinping, just days after ushering in the new year with a warning that his country may take an alternative path should the United States not ease economic sanctions, Reuters reported.
The trip - Kim's fourth to China since March - suggests negotiations over North Korea's nuclear arsenal may be regaining momentum after months without high-level diplomatic meetings.
Sean King, a former U.S. diplomat who is now senior vice-president of political strategy firm Park Strategies, said North Korea was using China as its security guarantee before the summit with Trump.
Dozens of security vehicles and officials blocked the roads around the train station in Dandong before the train passed, leading to speculation Kim was on board.
The South's Yonhap news agency cited an informed source late Monday saying that a special North Korean train had been seen crossing the border and was expected in Beijing Tuesday morning.
The visit also comes amid reports that negotiations are under way for a second summit between Kim and Trump.
South Korea's liberal President Moon Jae-in favors a negotiated solution to the North Korean nuclear confrontations.
In his annual New Year's speech last week, Mr Kim said he was committed to denuclearisation, but warned that he would change course if USA sanctions remained.
The United States has demanded that North Korea start taking crucial steps toward denuclearization, like declaring how many nuclear weapons it has and other details of its weapons program, for future inspections.
On Monday, the first day of the two-day vice ministerial-level trade talks, the U.S. missile destroyer sailed near a group of islands in the waters claimed by China, as part of the Pentagon's "freedom of navigation" operation aimed at challenging Beijing's military activities there.
"China has always supported North Korea and the U.S.to hold talks and to reach a positive outcome", Lu said. The last time they saw each other was six years ago in Pyongyang, according to Thae.
The NIS reportedly said Jo had not made with South Korean agents, but Kim wouldn't say if the agency told lawmakers his current location or whether he intends to defect.
Hanoi - about a four-hour direct flight from Pyongyang and in airspace over countries friendly to North Korea - boasts several top-class hotels.
"It's an obligation, not a choice, to defect to South Korea for North Korean diplomats like us as well as members of the Korean people", Thae said in a letter released on his website, which he claimed Jo often visited.
"Their behaviour has demonstrated that as well and we appreciate that", Pompeo said.
Possibly fearing the economic effect of crushing outside sanctions imposed over his weapons tests, Kim abruptly turned to diplomacy with Seoul and Washington a year ago.
Kim and Trump pledged to work towards denuclearisation at their landmark June summit in Singapore, but the agreement was short on specifics.
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