Prime Minister Shinzo Abe has asked South Korean President Moon Jae In to visit Japan before the planned summit between North and South Korea in late April, Japanese government sources said Tuesday.

He made the request during phone talks with Moon on March 16, but South Korea has yet to respond, and Moon may find it difficult to make time for a visit to Japan amid his preparations for the summit with North Korean leader Kim Jong Un on April 27, the sources said.

Abe wants to get Moon to raise with Kim the issue of North Korea's abductions of Japanese nationals in the 1970s and 1980s.

Abe has said resolving the abduction issue is one of his government's top priorities. Tokyo officially lists 17 citizens as having been abducted by North Korea, and suspects the country's involvement in other disappearances.

Five of the 17 were repatriated in October 2002, a month after the late North Korean leader Kim Jong Il admitted to the abductions of 13 Japanese nationals to the North in a landmark summit with then Prime Minister Junichiro Koizumi. Abe, deputy chief Cabinet secretary at the time, accompanied Koizumi to the summit in Pyongyang.

Tokyo seeks as well to deepen trilateral cooperation with the United States before President Donald Trump meets with Kim by the end of May.

At present, Moon is expected to visit Japan in May for a meeting of the leaders of Japan, China, and South Korea.

Another option under consideration is for Moon to visit Japan on a different occasion from the trilateral summit and ahead of the U.S.-North Korea summit scheduled to be held before the end of May, the sources said.

Abe's invitation for Moon to come to Japan follows his own visit to South Korea in February for the Pyeongchang Winter Olympics.

South Korea's Foreign Ministry has said the two countries have agreed to work toward arranging a trip by Moon separate from the trilateral summit.

In the meantime, according to government sources, Foreign Minister Taro Kono plans to meet Moon in South Korea next week and ask him to raise the abduction issue with Kim.

During talks with South Korean Foreign Minister Kang Kyung Wha in Washington in March, Kono requested that South Korea raise the abduction issue during the inter-Korean summit.

Japan has been calling for maximizing pressure on North Korea to abandon its nuclear and missile programs.