A joint team of police and military investigators has imposed travel bans on three civilian suspects accused of involvement in alleged drone flights to North Korea, sources said Friday.

The suspects include a graduate student in his 30s, surnamed Oh, who claimed to have flown the drones, an individual, surnamed Jang, suspected of building them, and a third person known to have worked at a drone manufacturing company set up by the other two, according to the sources.

The joint investigation was launched last week after North Korea claimed South Korea infringed on its sovereignty with drone incursions in September and on Jan. 4. South Korea's military has denied involvement, saying it does not operate the drone models in question.

The suspects are accused of flying a drone bound for North Korea from Ganghwa County, just west of Seoul. The aircraft reportedly took pictures of a South Korean Marine Corps base as it flew across the inter-Korean border.

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