FILE - In this Nov. 27, 2017, file photo, North Korean soldiers look at the South side as a South Korean stands guard near the…
In this Nov. 27, 2017, file photo, North Korean soldiers look at the South side as a South Korean stands guard near the spot where a North Korean soldier crossed the border on Nov. 13 at the Panmunjom, in the Demilitarized Zone, South Korea.

SEOUL - South Korea says it has fired warning shots to repel a North Korean merchant ship that violated their disputed western sea boundary.

South Korea's military says it believes the North Korean ship crossed the sea boundary on Wednesday due to bad weather and an engine problem.

It says it's the second time that South Korea has fired warning shots to drive back a North Korean ship in the area since South Korea's current liberal government took office in 2017. The first incident happened in September.

Ties between the two Koreas are strained amid a stalemate in U.S.-led diplomacy on ending the North Korean nuclear crisis.

North Korea said Monday its troops conducted artillery firing drills near the sea boundary, drawing formal protests from South Korea.