SEOUL (AFP) — South Korean police on Friday arrested six Americans attempting to send plastic bottles packed with rice and Bibles to North Korea, the head of the investigation team said.

Local police said the six were trying to send thousands of plastic bottles, filled with rice, one-dollar bills and Bibles, into the sea off Ganghwa Island at 1:03 a.m. on Friday when they were caught.

“We have arrested and are questioning six American nationals in their 20s to 50s on suspicion of violating the Framework Act on the Management of Disasters and Safety,” the head of the investigation team at Ganghwa Police Station in Incheon told Agence France-Presse.

The Americans could not speak Korean, so “an interpreter was provided for them and we have since started the questioning,” he added.

Located northwest of Seoul, Ganghwa Island is one of the closest South Korean territories to North Korea, with some parts of the surrounding sea lying just 10 kilometers from the maritime border between the two countries.

The island has long been a popular site for non-profit organizations and anti-North Korean groups to launch plastic bottles filled with rice, as well as USB sticks containing K-pop and South Korean dramas.

The area was designated a danger zone last November, along with other border regions where activists launch balloons carrying leaflets.

At the time, the government said such activities could be perceived by the North as provocative.

Last year, the two Koreas were in a tit-for-tat propaganda war, as the North sent thousands of trash-filled balloons southwards, saying they were retaliation for propaganda balloons launched by South Korean activists.

In response, Seoul turned on border loudspeaker broadcasts — including K-pop tunes and international news—and North Korea started transmitting bizarre, unsettling noises along the frontier that had been a major nuisance for South Korean residents in the area.