美国有线新闻 CNN 金正恩对中国进行非正式访问 与习近平主席举行会谈（在线收听）

A heavily armored train pulled into a station in the Chinese capital of Beijing earlier this week, increased security there. The removal of tourists from the area and the fact that the train looked like one that North Korea's leaders have used on trips abroad all led observers to speculate that North Korean dictator Kim Jong-un was on it.

They were right. He was there to meet with Chinese President Xi Jinping. The North Korean leader is also supposed to meet with U.S. President Donald Trump in the months ahead but a date hasn't been set for that.

Some U.S. officials say the fact that Mr. Kim engaged in diplomacy with China could mean it's more likely he'll follow through in talks with America. Others see it as a sign that China may try to play a role in talks between North Korea and the U.S.

So, the full significant of this trip isn't known yet. But it did c?a??tch other countries by surprise.

IVAN WATSON, CNN SENIOR INTERNATIONAL CORRESPONDENT: China and North Korea dropped the diplomatic bombshell on Wednesday, simultaneously confirming that North Korea's leader made a secret four-day visit to China. They waited until after the meeting was over and after the special train carrying Kim Jong-un crossed the border back into North Korea to reveal that the visit took place.

This is Kim's first foreign trip since he assumed the throne in Pyongyang more than six years ago. China is North Korea's oldest ally, but the relationship has been frosty for years, especially after multiple North Korean nuclear weapons test and missile launches were all banned by the United Nations.

In Beijing, China's leader gave Kim and his wife the red carpet treatment. Xi Jinping called their alliance a strategic choice that shouldn't change because of individual incident.

As for Kim, he suggested denuclearization on the Korean peninsula could be possible if the U.S. and South Korea cooperate.

This is the surprise beginning to what's expected to be a busy period of high level diplomacy for North Korea's young leader. He's scheduled to hold the summit with the South Korean president in April and sometime after, he may make history with a face to face meeting with President Trump.

The White House quick to claim credit for Kim's trip to Beijing, arguing it's the result of the so-called maximum pressure campaign to impose economic sanctions on Pyongyang. If all goes according to plan, Kim will rapidly go from extreme international isolation to sitting down at the negotiation table with the leaders of the two most powerful nations on the planet.

Ivan Watson, CNN, Seoul.