Isao Iijima, a senior adviser to Japanese Prime Minister Shinzo Abe, was tightlipped about the subjects of his discussions when he arrived at the airport in Beijing.
"By visiting there, I was able to hold sincere talks for a long time," Iijima, a political fixer, told reporters in the Chinese capital, according to Jiji Press.
"I have no plan to grant interviews. I want to closely examine (what was discussed) and consider it," he said.
The Japanese government has refused to discuss Iijima's visit, despite coverage of it by the North's official Korean Central News Agency (KCNA).
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Iijima was a senior aide to Japan's former prime minister Junichiro Koizumi, and is known to have played a role in organising his trips to Pyongyang in 2002 and 2004 for talks with then-North Korean leader Kim Jong-Il.
The North's state media showed footage of Iijima's talks yesterday with Kim Yong-Nam, North's Korea's ceremonial head of state, according to Japan's national broadcaster NHK today.
In it, Kim said he appreciated Iijima's work on bilateral relations.
Kim's translator was also seen saying in Japanese that Iijima returned to Pyongyang with an extremely important mission, NHK said.
Japanese government ministers, from Prime Minister Abe on down, have refrained from discussing Iijima's visit to the North, including its purpose and the length of his stay.