North Korea accuses South Korea of a “serious provocation” after South Korean troops fired warning shots Tuesday at North Korean soldiers setting up barriers along their tense border.

North Korean troops, who were working on construction and maintenance in the area, did not heed broadcasted messages to halt, an investigation said.

South Korea’s president, Lee Jae Myung, announced plans to end some military activities along its border with North Korea and restore a 2018 military agreement with its neighbor.