A train believed to be carrying a senior North Korean delegation has left the Chinese capital following a dramatic whirlwind visit that some reports said included the country's leader Kim Jong-un.
The conservative South Korea Chosun Ilbo newspaper, citing an unnamed senior intelligence official, said the delegation had included Kim and that he had since left to return to North Korea.
South Korea's left-leaning press Hankyoreh also reported Kim had travelled to Beijing for meetings with Chinese President Xi Jinping on Monday afternoon before leaving for a "third location" on Tuesday. It did not cite specific sources.
The Hankyoreh did not specify where the "third location" was but said it could be in China.
South Korea said it was closely watching events in Beijing, where a foreign ministry spokeswoman deflected a question on whether Kim, his sister or some other senior North Korean was visiting. South Korea's spy agency declined to confirm the report.
"At present I have no understanding of the situation you mention. If there is news we will release it," foreign ministry spokeswoman Hua Chunying told a regular daily briefing.
Diplomatic sources in Beijing said a senior North Korean official was in town, but did not know exactly who.
Bloomberg, citing three unidentified sources, reported late on Monday that Kim was in Beijing in what would be his first known trip outside North Korea since taking power in 2011.
The unconfirmed visit came ahead of planned summit meetings with South Korean President Moon Jae-in and US President Donald Trump.
"The presidential Blue House is watching things in Beijing very closely, while keeping all possibilities open," said the senior official in Seoul, who spoke on condition of anonymity.
Improving ties between North Korea, which is pursuing nuclear and missile programs in defiance of UN Security Council resolutions, and China would be a positive sign before the planned summits, he said.
A Reuters reporter saw a convoy leave Beijing's Diaoyutai State Guest House, where senior foreign leaders often stay, and drive north on Tuesday morning. It was unclear where the convoy was headed.
Later, a Reuters journalist saw what was believed to be the delegation's train pulling out of a Beijing station. The group was reported to have arrived in China on Sunday after crossing from North Korea in the border city of Dandong.
A senior US official who follows North Korea closely said the available evidence suggested Kim travelled to Beijing to meet Chinese President Xi Jinping, but stressed that has not been confirmed.
One source with ties to China's leadership said it was possible Kim's younger sister, Kim Yo Jong, was in town. She visited South Korea for the Winter Olympics last month, paving the way for a summit between the two Koreas.
Xi and Kim Jong-un had reasons to meet in advance of Kim's meetings with Moon and possibly Trump, the US official said.
"Xi has met Trump, and in many respects learned how to deal with him better than some people here do," the official said.
The rail journey between Dandong and Beijing covers more than 1100km and takes at least 14 hours by ordinary service, according to Chinese railway timetables.
