The Korean Central News Agency released a statement on Monday, confirming the meeting after it was announced last week by the Kremlin. He noted that the North's moratorium on nuclear tests and scaling down of U.S.
"Russia shares our viewpoints such as the achievement of complete denuclearisation on the Korean Peninsula and the settlement of permanent peace", foreign ministry spokesman Kim In-chul said at a briefing in Seoul.
Ushakov met last week in Moscow with Fiona Hill, a foreign policy adviser to Trump, for talks on North Korea.
After the failed Hanoi summit, Kim is probably looking to prove that he is still sought after by world leaders, and that he has more options, said Artyom Lukin, a professor at Far Eastern Federal University.
Russia's Ria Novosti news agency quoted sources in the country's rail service as saying a train carrying Kim was expected to arrive at Vladivostok station at 6:00 pm local time (0800 GMT) on Wednesday.
Kim had two summits with U.S. President Donald Trump, but the latest one in Vietnam in February collapsed because North Korea wanted more sanctions relief than the United States was willing to give for the amount of nuclear disarmament.
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Unlike her brother, who will take up to a day to reach his destination, Chosun reported that Kim Yo-jong "boarded a flight in Pyongyang for Vladivostok in the morning" on Monday; the flight takes less than two hours.
Where Kim's train will stay after arrival is being kept secret, it added.
Reports placed Kim Chang Son at the famous Mariinsky ballet theater, the headquarters of Russia's Pacific naval fleet, and an aquarium in the city. "It's part of his plan to continue work on diplomacy with everybody else, to put pressure on Washington", said Sue Mi Terry, senior fellow at the Center for Strategic and International Studies in Washington.
Kim, like his father, avoids air travel and is likely to travel to Vladivostok by train.
The summit will be the first between Putin and the North Korean leader and the nuclear row, and how to resolve it, would be the main item on the agenda, Kremlin aide Yuri Ushakov told reporters. There are some indications that the meeting will be held in the far-eastern port of Vladivostok, not too far from Russia's border with the North.
Denyer reported from Seoul.