One such train was spotted on Monday heading north, near where the borders of North Korea, Russia and China meet.
It was moving in the direction of Vladivostok, where Mr. Putin is attending an economic forum.
On Tuesday, North Korean state media confirmed that Mr. Kim had indeed left Pyongyang, the North’s capital, for Russia by train.
South Korean officials said soon afterward that he had crossed the border.
The green train that officials look for is the special bulletproof one that Mr. Kim — and his father and grandfather, who ruled North Korea before him — have used to visit China, Russia or the former Soviet Union.
Persons:
Kim Jong, —, Vladimir V, Putin —, Putin, Mr, Kim, Kim —, Kim’s
Organizations:
Soviet Union
Locations:
Russia, North Korea, China, Vladivostok, North Korean, Pyongyang