Seoul, South Korea – South Korean forces fired warning shots at a North Korean merchant vessel that crossed the disputed sea border between the two countries in the Yellow Sea for up to an hour, officials said.

The North Korean vessel crossed the Northern Limit Line (NLL) near the South Korean border island of Baengnyeong at about 5am local time on Friday (20:00 GMT) and remained on the southern side of the maritime frontier for an hour while also advancing up to 5km (3.1 miles) south of the demarcation line, South Korea’s military said.

“Our military broadcasted a warning and fired warning shots, after which the North Korean merchant ship retreated from our territorial waters,” South Korea’s Joint Chiefs of Staff (JCS) said in a statement.

“Our military closely monitored North Korea’s movements and responded in accordance with operational procedures,” the JCS said.

The North Korean ship retreated from the South’s maritime control area after dozens of warning shots were fired by the South Korean military, according to authorities who also reported that a South Korean navy convoy was conducting operations in the area at the time of the border breach.

The incident also takes place as North Korea’s Vice Foreign Minister Kim Son-gyeong is scheduled to attend the 80th United Nations General Assembly meeting in New York.

North Korea has not yet commented on the incident.

“We will firmly maintain our readiness posture and respond resolutely to any situation to safeguard the NLL,” the JCS added in its statement.

Friday’s incident marks the first intrusion beyond the NLL by a North Korean vessel in three years.

In October 2022, a North Korean merchant vessel also violated the demarcation line and was chased away by warning shots from a South Korean warship.

North Korea’s military also fired 10 rounds of artillery shells as warning shots towards the South’s territorial waters in response.

The disputed sea boundary off the Korean Peninsula’s west coast is a source of long-running animosities between the two countries and has led to several fatal confrontations, including North Korea’s shelling of a South Korean island in 2010 and the North’s alleged torpedoing of a South Korean navy ship that killed 46 sailors the same year.

As the de facto maritime border between the Koreas, the NLL was drawn up after the 1950–53 Korean War, but it is not recognised by North Korea, which claims the sea border is further to the south of the current boundary line.

Last year, North Korean leader Kim Jong Un denounced the sea boundary as “illicit and lawless”, while calling for a redefining of his country’s borders.