Another North Korean fishing boat violated the Yellow Sea maritime border with South Korea on Tuesday night.

The South Korean Joint Chiefs of Staff(JCS) said the ship crossed some 700 meters over the Northern Limit Line at 9:40 p.m. but retreated quickly when a high-speed South Korean naval vessel approached and broadcast radio warnings.

A JCS official explained it’s unusual for a North Korean fishing ship to cross over the line at night.

This is the seventh time North Korean fishermen have violated the maritime border this month.