This image shows a protest by Greenpeace activists atop a pole on a 2,999-ton LPG tanker. (The Coast Guard)

Police have detained four foreign Greenpeace activists for questioning after they illegally boarded an LPG tanker and staged a protest demanding a reduction in plastic production, officials said Sunday.

The Coast Guard in Pyeongtaek, 65 kilometers southwest of Seoul, said the four were detained for questioning on charges of vessel trespassing and obstruction of official duties.

The activists are accused of illegally boarding a 2,999-ton LPG tanker off the coast of Incheon at 10:42 a.m. the previous day, painting on the hull and staging a protest atop a 12-meter pole on the deck.

The activists were demanding a reduction in plastic production as the fifth round of the Intergovernmental Negotiating Committee on Plastic Pollution (INC-5) was under way in the southeastern port city of Busan from Monday, to find ways to eliminate plastic waste.

Coast Guard forces brought them down around 12 hours after they boarded the vessel, at 10:25 p.m. on Saturday, and transferred them to the Coast Guard agency in Pyeongtaek for investigation after detaining them at the scene. (Yonhap)