North Korean leader Kim Jong Un was expected to meet Tuesday with China's president at the start of a visit to Beijing believed to be an effort to co-ordinate with his only major ally ahead of a possible second summit with U.S. President Donald Trump.
Kim was invited by Xi and accompanied by his wife Ri Sol Ju and several top officials on his train journey across the border, the state-run Korean Central News Agency said.
"Kim's confidence stems from the expectation of growing and reliable support by China", Rudiger Frank, a professor of East Asian economy and society at the University of Vienna, wrote on the North Korea-watching 38 North blog on January 2.
Kim's trip coincides with the second day of talks between United States and Chinese officials in Beijing aimed at resolving their trade war, but China rejected the notion that it was using the North Korean issue as a bargaining chip in the negotiations.
There is speculation that he is seeking advice from Xi as he prepares for further denuclearization talks with Trump.
"If the United States does not keep the promise it made in the eyes of the world, and out of miscalculation of our people's patience, it attempts to unilaterally enforce something upon us and persists in imposing sanctions and pressure against our Republic, we may be compelled to find a new way for defending the sovereignty of the country and the supreme interests of the state", Kim said.
Four of Kim's trips have been to China, signaling its importance to North Korea. Kim may also seek China's support amid tight global and USA sanctions on North Korea.
South Korea's Yonhap, without identifying its sources, said the two leaders held talks for an hour in which they discussed the second U.S.
"With Chinese and USA officials meeting to discuss how to end the growing trade war between the two superpowers, it shows Beijing clearly has a North Korea card to play if it sees fit".
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China's official Xinhua News Agency issued a nearly-identical report, while Beijing's North Railway Station was cocooned in security, with dozens of police and paramilitary troops patrolling outside.
"Kim will take advantage of the trade and other disputes between the US and China, he is also going to take advantage of Trump's domestic troubles and squeeze compromise from Trump in the next meeting". Kim met twice with Xi a year ago beforemeeting with Donald Trump in Singaporein a historic summit that ended up achieving very little.
Following his first visit, North Korea's Ministry of Foreign Affairs released a statement noting that Kim had pledged to "steadily carry forward and develop the Sino-DPRK friendship which the leaders of elder generations personally provided and nurtured with sincerity in the course of contributing to the victorious advance of the socialist cause, out of common ideal, faith and deep revolutionary friendship".
Washington is pressing North Korea to offer up a detailed accounting of its nuclear arsenal, while the North says it has already done enough and it's time for the U.S.to ease the harsh worldwide sanctions that hold back the North Korean economy.
USA and Chinese officials are also holding trade talks in Beijing this week after agreeing on a temporary truce to their trade war last month. However, Xi has called on the sides to "meet each other halfway", and China's foreign minister in September urged some form of sanctions relief in response to any positive outcomes from the first Kim-Trump summit.
The US president said last week he had received a "great letter" from the North Korean leader but declined to reveal its contents.
"As to whether this is used as a bargaining chip by China in trade talks, I believe more Americans would think so than Chinese do", the tweet went on to say.
A declaration to end the Korean War, a formal peace treaty and the establishment of bilateral relations between North Korea and the United States are seen as the kind of security guarantees that can be offered by Washington to Pyongyang if it denuclearizes.
Ties between China and North Korea, which had frayed as Pyongyang stepped up its missile and nuclear tests up to late 2017, warmed over the past year as Kim engaged with China, South Korea and the United States.