When Seoul was preparing to open a liaison office in the North Korean city of Kaesong this summer after a decade of virtually no contact with its longtime enemy, South Korean officials had heated debates over whether they should seek approval from Washington.

Some top aides to President Moon Jae-in stressed it was an issue for the two Koreas alone and there was no need to involve their U.S. ally, two people with knowledge of the situation said.

But to the surprise of several officials at the meeting, Unification Minister Cho Myoung-gyon argued Washington must be consulted because Seoul's plans might run afoul of sanctions imposed on North Korea over its nuclear weapons program.