Japan is expecting tens of thousands of North Korean refugees to try to reach its coasts in wooden boats if war breaks out on the Korean peninsula and is considering building a temporary shelter for them in Kyushu, the Yomiuri Shimbun reported last week.

But the facility in Japan’s southernmost island will also be used to determine if such refugees include North Korean agents or terrorists sent to infiltrate the country.

“If North Korean agents or terrorists successfully enter the country disguised as evacuees, it is feared they could target vital facilities such as those of US Forces Japan, the Self-Defense Forces and nuclear power plants,” the Yomiuri said in a story picked up by South Korea’s Chosun Ilbo.

Japanese authorities also plan to increase security patrols along the Japan’s coastline to intercept North Korean agents attempting to land by sea.

Using refugee columns to hide disguised troops was a common tactic of North Korean forces during the Korean war. North Korean spy vessels and small submarines have also reportedly penetrated Japan’s waters and coastlines.