A train believed to be carrying high-level North Korean officials departed a Beijing station Tuesday as rumors indicated that Kim Jong Un may have been aboard.

Japan’s Kyodo News reported that the train had departed, but it didn’t clarify how it learned of the departure. The news agency reported that security around the Chinese capital continued to be extra tight.

Reports of the train arriving in Beijing first surfaced when photos emerged from the station. Japan’s NTV and public broadcaster NHK said heavy security was seen in video and photos suggested a high-level official was aboard.

Monday's arrival sparked speculation that the North Korean despot was on board the train. The train may have traveled through the northeastern Chinese border city of Dandong, according to Kyodo News. Sources told Bloomberg that Kim was visiting Beijing, though further details were not provided.

China's Foreign Ministry spokeswoman Hua Chunying told reporters Tuesday that she knew they were "all very curious" about Kim's possible visit to the country, but she had "no information" regarding his or any North Korean official's potential visit.

The White House said in Monday's press briefing it could not confirm reports of Kim's potential visit to Beijing. A spokeswoman for the Chinese Foreign Ministry said she was not aware of the situation and had no further comment. North Korea's state-run media had no reports of a delegation traveling to China.

There was also heavy security reported at the Friendship Bridge before it crossed from North Korea to China. To deepen the mystery, a motorcade of black limousines was also seen waiting at the train station. Rows of Chinese soldiers appeared to be marching on the platform.

Kim is expected to have a summit meeting with South Korean President Moon Jae-in in late April and with President Trump in May.

There had been no word of Kim planning a summit with Beijing, however. China has been one of North Korea's most important allies, but relations have grown chilly because of Kim's development of nuclear weapons and long-range missiles.

Kim’s late father, Kim Jong Il, visited Beijing in 2011. The late leader also took a similar green and yellow train that was spotted on Monday for his son’s visit. This would be the first known visit to an outside country for Kim since he assumed power in 2011.

The Associated Press contributed to this report.