North Korean leader Kim Jong Un met in secret with China’s Xi Jinping this week in Kim’s first trip abroad since assuming power, Chinese state news reported Wednesday.

The news confirms widespread rumors that Kim had unexpectedly traveled to China via an armored train on Monday in his first foreign trip as leader of the North. The 21-car behemoth chugged into Beijing’s central train station, where a military honor guard and a large motorcade of diplomatic vehicles reportedly met it. But senior officials in the U.S., South Korea and China declined to comment on exactly who was thought to be in the carriages.

The news of Kim’s visit was only officially confirmed after the same train left Beijing. Yang Jiech, a leading Chinese diplomat, will brief South Korean officials on Thursday about the meeting, South Korea’s government said.

President Donald Trump said he heard from Xi on Tuesday night.

“His meeting with KIM JONG UN went very well and that KIM looks forward to his meeting with me,” Trump tweeted Wednesday. In the meantime, and unfortunately, maximum sanctions and pressure must be maintained at all cost!

China’s state-run Xinhua News Agency said Kim made the unofficial visit at Xi’s request, just weeks before the North Korean leader is expected to meet with U.S. President Donald Trump. Kim was also accompanied by his wife, Ri Sol-ju, and his senior advisers.

The meeting is a new development in the diplomatic saga on the Korean peninsula. Kim met with envoys from South Korea earlier this month, who later said the North Korean government was open to holding talks with the United States.

Chinese media reported that Kim expressed a similar willingness for dialogue during his meeting with Xi.

“The issue of denuclearization of the Korean Peninsula can be resolved, if south Korea and the United States respond to our efforts with goodwill, create an atmosphere of peace and stability while taking progressive and synchronous measures for the realization of peace,” Kim Jong Un was quoted as saying in Xinhua News. The outlet also said Kim hoped to “develop friendship” with China following the meeting.

It’s unclear where a summit between Kim and Trump would take place. Until this week, Kim had never crossed North Korean borders. A sitting U.S. president has never traveled to the country.