Japan is considering informal talks with North Korea on the sidelines of an international security forum in Mongolia next week after a historic U.S.-North Korea summit, government sources said Friday.

As Prime Minister Shinzo Abe has expressed his willingness to hold direct talks with North Korea, Tokyo hopes to lay the groundwork for realizing such a meeting and resolving the issue of Japanese nationals abducted by Pyongyang decades ago, according to the sources.

Abe has placed priority on resolving the abduction issue and U.S. President Donald Trump has promised to raise it during his June 12 meeting with North Korean leader Kim Jong Un in Singapore.

Japan plans to send a senior official from the Foreign Ministry's Asian and Oceanian Affairs Bureau to the Ulaanbaatar Dialogue from June 14 and 15.

On the fringes of the security forum, the official at the deputy director general level is expected to talk with a senior official from the Disarmament and Peace Institute, North Korea's Foreign Ministry think tank, the sources said. The Mongolian government has been serving as an intermediary.

Tokyo is expected to explore contacts with Pyongyang in the months ahead.

(Japanese Prime Minister Shinzo Abe, left, and North Korean leader Kim Jong Un)

The most immediate opportunity may come next week when the U.S.-North Korean summit is held in Singapore as the government plans to send Abe's national security adviser Shotaro Yachi and Kenji Kanasugi, who heads the Asian and Oceanian Affairs Bureau.

In August, a foreign chiefs' meeting could be arranged between Japan and North Korea on the sidelines of an international meeting in Singapore.

If Kim, accepting an invitation from Russia, takes part in an economic forum in September in Vladivostok in the Russian Far East, Abe may seek to meet with the North Korean leader.

Through such exchanges in third countries, the Japanese government would explore the possibility of an Abe-Kim summit in either Tokyo or Pyongyang.

"I would like to directly face North Korea and talk with (Kim) so as to achieve an early resolution of the abduction issue," Abe said Thursday after meeting with Trump at the White House.

Since Trump expressed in March his intention to meet with Kim, Tokyo has conveyed through multiple channels to Pyongyang it hopes to resume bilateral talks.

Japan will urge North Korea to follow through on a 2014 bilateral agreement under which Pyongyang agreed to reinvestigate the whereabouts of all of the abductees, the sources said.

It is also expected to explain its basic stance that the normalization of bilateral ties and the extension of economic support will not come unless the abduction, nuclear and missile issues are resolved in a comprehensive manner, according to the sources.