The U.S. has discouraged Tokyo from becoming too close with Pyongyang, with Secretary of State John Kerry warning his Japanese counterpart about high-level visits to North Korea, several Japanese news sources have reported.

Reports have stated that Kerry and Japanese Foreign Minister Fumio Kishida spoke over the phone on July 7, with Kerry insisting on proper discussions prior to any visit by Prime Minister Shinzo Abe to North Korea.

Kerry informed Kishida that prior notification alone would not be sufficient, the reports indicated.

Japan and North Korea, who have no official ties and