China has expelled numerous Korean missionaries in recent months, according to media reports.

The Chinese government expelled 32 Korean missionaries from Yanji, South Korean media said.

The South Korean government confirmed that these missionaries had been arrested, according to Bretibart.

Some were expelled after officials raided their homes and simply asked them to leave the country, Agence France-Presse reported.

“In the past, most missionaries were given a month to leave since their activities in China were not harming the country. This time, it was different,” one source told the Financial Times.

Though it is unclear exactly why the country decided to expel the missionaries, officials reportedly cited problems with their visas.

Some say that the expulsions may have come in response to rising tensions amid South Korea’s support for the U.S. military’s Terminal High Altitude Area Defense system (THAAD), while others point to the increasing crackdown on Christians and churches that the Chinese government had been carrying out, such as by taking down the churches’ crosses.

“There was no official explanation from China,” one anonymous official told Reuters. “There is no confirmation that it is related to Thaad.”

Tensions have grown in China for Christians since 2015, when the government increased scrutiny on churches. Over the past few years, many house churches have been closed down, crosses of churches have been taken down, and Christians and activists have been detained.

Many missionaries in China specifically focus on providing aid to North Koreans who flee from their home country into China.