SEOUL, South Korea — North Korea on Saturday escalated its attempt to create a rift between South Korea and the United States, as Washington sent mixed signals over whether it would tighten or relax sanctions on the North.

Ever since the summit meeting between the North’s leader, Kim Jong-un, and President Trump in Hanoi, Vietnam, late last month abruptly ended without a deal, North Korea has ceaselessly urged South Korea to distance itself from the United States and to push ahead with joint economic projects that have been held back by American-led United Nations sanctions.

North Korea’s official trade has been devastated by international sanctions imposed since 2016. The country has tried to circumvent them by importing refined fuel or exporting coal through ship-to-ship transfers on the high seas, a move banned under United Nations sanctions. It has also sought to undermine the sanctions by boosting economic cooperation with South Korea.

President Moon Jae-in of South Korea remains eager to boost inter-Korean economic ties, raising fears at home and abroad that he may steer his government away from international efforts to enforce sanctions against the North. But in reality, Mr. Moon’s hands are tied unless the United States and North Korea reach an agreement on denuclearizing the North and Washington helps to ease sanctions.