South Korean Foreign Minister Kang Kyung-wha spoke by phone with her U.S. counterpart Rex Tillerson on Saturday night, according to the ministry.
Presidents Moon Jae-in and Donald Trump are to meet in Seoul next month. Their summit comes as tensions have heightened in the wake of the North's sixth nuclear test last month and a series of ballistic missile launches.
Korean political commentator Jung-sik Seo anlyses the upcoming summit.