An adviser to Japanese Prime Minister Shinzo Abe has ended a visit to North Korea but would not give details of his talks with leaders in Pyongyang.

Isao Iijima's three-day visit came amid a slight easing of tension on the Korean Peninsula after weeks of threats from the North aimed at Washington, Seoul and Tokyo.

Japan has not disclosed the purpose of Iijima's trip. He told reporters in Beijing that he had long, serious talks with North Korean officials, but refused to say anything more.

Iijima also was a senior aide to former Japanese Prime Minister Junichiro Koizumi, who met with late North Korean leader Kim Jong Il in 2002 and 2004.

Tokyo officials hinted Iijima's visit was related to cases of Japanese kidnapped by the North decades ago.