South Korea held a routine military exercise near a disputed border with North Korea Monday, despite the North's threat of retaliation if the border is violated.

The drill included artillery, mortars and helicopters.

An announcer on a radio broadcast from the North warned of an immediate and merciless counter-attack if even a “single column of water” is monitored in North Korean waters during the drill.

“Once the group of traitors starts a reckless military provocation in those waters, trespassing on the DPRK's (Democratic People's Republic of Korea) inviolable marine demarcation line, and in case just a single column of water is observed in its territorial waters, the Korean People's Army will promptly make merciless retaliatory strikes.”

The North warned inhabitants of five front-line islands to evacuate to avoid possible retaliatory shelling.

No action from the North has been reported.

South Korea and the U.S. are holding a joint anti-submarine drill in the Yellow Sea this week.

Beginning next Monday, the two allies will begin the first of two annual large-scale war games involving thousands of troops from both countries.

South Korea regularly conducts artillery exercises from front-line islands near the disputed border off the west coast of the Korean Peninsula. One drill in November of 2010 triggered a North Korean artillery bombardment that killed four South Koreans on the island of Yeonpyeong.

U.S. military officers tell VOA that threats of retaliation against South Korean military drills are common and no cause for alarm.