Thirty-two South Korean missionaries were expelled from China’s border region with North Korea last month, reports The Guardian.

The 32 were based in China’s north-eastern Yanji region and many of them had worked there for more than a decade, South Korean media have reported.

South Korea’s foreign ministry says it has advised Christian groups about the importance of complying with the laws and customs of the areas where they work. There are thought to be over 1,000 South Korean missionaries in China, most working in the northeast, where some help defectors from North Korea to travel to third countries, including South Korea.

“This act is seen as a retribution for the South Korean government’s decision to deploy an American missile defense system called THAAD, but will have repercussions for North Korean refugees living and/or hiding in this part of China as well. Allegedly, among other tasks the expelled served those refugees,” says Thomas Muller, analyst for Christian charity Open Doors.

Meanwhile, the North Korean leader’s half-brother has reportedly been killed. Kim Jong-nam, the eldest brother of Kim Jong-un, was found dead in an airport in Kuala Lumpur. South Korea’s Chosun TV reported that two female North Korean agents used poison needles to kill him.