South Korea sent two helicopters to battle a wildfire inside the Korean Demilitarized Zone (DMZ), Seoul’s military said Friday, adding it had warned North Korea in advance of its firefighting mission along the heavily armed border area.

In June last year, North Korean troops violated the border three times, prompting South Korea to fire warning shots. The incidents occurred when the Koreas were embroiled in Cold War-style campaigns like balloon launches and propaganda broadcasts, but they didn’t develop into a major source of tensions.

South Korean soldiers fired warning shots at North Korean troops after nearly a dozen crossed the demilitarised zone separating the warring nations.