A top presidential official said on Saturday that United States officials have expressed concern that tensions between South Korea and Japan over Tokyo's export curbs against Seoul are not conducive to trilateral cooperation between the three countries.

Kim Hyun-chong, deputy chief of Cheong Wa Dae's National Security Office, made the remark to reporters as he wrapped up a four-day visit to Washington that included meetings with top officials.

At Dulles International Airport in Washington, Kim said that he met with people in the U.S. administration, Congress and think tanks, and explained the unfairness of Japan's unilateral measure and the effects that this unfair measure has on the security situation among the South, the United States and Japan.

The NSC official said all the people he has met shared the understanding about the concerns over tensions between Seoul and Tokyo and that is why the State Department said it is going to do everything it can to maintain cooperation among the three nations.

Kim, however, said U.S. officials have not talked explicitly about "mediation."

During the U.S. trip, Kim met with acting White House chief of staff Mick Mulvaney, U.S. Trade Representative Robert Lighthizer and Deputy National Security Adviser Charles Kupperman.