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

North Korea accused South Korea of a “dangerous provocation” during a recent incident at the border of the two countries, adding to tensions as Pyongyang chafes at the annual joint US-South Korean military drills that are underway.

Report comes a day before US President Donald Trump’s summit with his South Korean counterpart, Lee Jae-myung.