The United States has urged Prime Minister Shinzo Abe to refrain from visiting North Korea, with Secretary of State John Kerry warning such a trip could disturb trilateral coordination involving Tokyo, Washington and Seoul to rein in Pyongyang's missile and nuclear programs, sources familiar with Japan-U.S. relations said Tuesday.

In a telephone conversation with Foreign Minister Fumio Kishida on July 7, Kerry requested that Japan hold behind-the-scenes consultations with the United States in advance should Tokyo consider a visit to North Korea by Abe, according to the sources.

The top U.S. diplomat also expressed displeasure over Japan's policy of gradually lifting its unilateral sanctions on North Korea depending on progress in the new round of investigations into the fate of Japanese nationals abducted by the North in the 1970s and 1980s.