SEOUL—South Korean President Lee Myung-bak vowed Monday to strike back at any further attacks by North Korea on South Korean territory, but the South’s military later canceled a drill that would have asserted its territorial rights over a maritime border the North disputes.

The military late Monday initially announced it would conduct an artillery drill on the same island attacked last Tuesday by the North in an hourlong barrage that killed four South Koreans, destroyed more than 30 homes and damaged nearly every building in the island’s main village, which was home to 1,400 people.

The new test was announced shortly after 7 p.m. Monday, then canceled about 90 minutes later without explanation. The test could have led to another confrontation with North Korea and, as a result, its cancellation underlined the constraints Seoul faces in dealing with Pyongyang’s latest aggression