The Japanese Embassy in Seoul is the target of regular, generally peaceful demonstrations against South Korea's former colonial master, but early Monday morning a man vented his anger by ramming his truck into the main gate of the embassy.

The man, a Mr. Kim in his 60s, was immediately arrested and remains under investigation. The gate was forced back by the blow but no other damage or injuries were reported. The South Korean government offered an expression of regret to the Japanese Embassy and said it would tighten security...