North Korea’s Coast Guard is known to have drastically stepped up its patrol to prevent its citizens from defecting by sea.

A high-level source said North Korean patrol boats have stopped monitoring illegal fishing by Chinese fishing vessels in waters near the Northern Limit Line (NLL) and are instead focusing on patrolling the coast. The NLL is the maritime border between the two Koreas.

The source believes the stepped-up patrol is to prevent North Koreans from defecting by the Yellow Sea, as the number of defectors continues to rise.

The coast guard policing land under the command of North Korea’s 4th Corps has also reportedly increased its monitoring of citizens who may be planning to defect.