The South Korean government expressed regret over a local religious group sending Bibles attached to large balloons across the border into North Korea.

Unification Ministry deputy spokesperson Cho Hye-sil said Friday the government is regretful about the campaign by Voice of the Martyrs Korea, which comes after the South vowed to crack down on such tension-building activities.

The spokesperson said an investigation into the incident has been launched, while related agencies are expected to take appropriate punitive measures.

Earlier in the day, the missionary group claimed that it sent four Bible-carrying balloons towards the North from the northwestern city of Incheon the night before.

The group was previously forced to cancel plans to send rice to the North after facing opposition from nearby residents.