SEOUL (Reuters) - China has expelled 32 South Korean Christian missionaries, a Korean government official said on Saturday, amid diplomatic tension between the two countries over the planned deployment of a U.S. missile defense system in the South.

FILE PHOTO: A Terminal High Altitude Area Defense (THAAD) interceptor is launched during a successful intercept test, in this undated handout photo provided by the U.S. Department of Defense, Missile Defense Agency. U.S. Department of Defense, Missile Defense Agency/Handout via Reuters/File Photo

The 32 were based in China’s northeastern Yanji region near the border with North Korea, many of whom had worked there more than a decade, South Korean media have reported.

South Korea’s foreign ministry said on Friday it briefed Christian groups on the case of the missionaries, adding that they were expelled in January.

The ministry advised the groups on the importance of complying with the laws and customs of the areas where they work, it said.

On Saturday, a South Korean missionary in Seoul who insisted on anonymity told Reuters that four people, including a Korean missionary and a Korean-American pastor, were apprehended by Chinese police in a Yanji hotel on Feb. 9.

The South Korean official who talked about the 32 expulsions confirmed that one Korean man, whom he did not identify, had been arrested in China for possible immigration violations.

“We will provide consular services for him as needed,” the official said, without giving details.

The official did not comment on whether three other people had been detained.

RETALIATION?

In South Korea, China is widely believed to be retaliating against Seoul’s plan to host the Terminal High Altitude Area Defence (THAAD) system of the U.S. military, against the threat of the missile attack from North Korea.

But there was no indication of a direct link between the expulsions and tension over THAAD, said the official.

“There was no official explanation from China,” he said. “There is no confirmation that it is related to THAAD.”

China’s Communist Party says it protects freedom of religion, but keeps a tight rein on religious activities and allows only officially recognized religious institutions.

The number of Korean missionaries working in China might top 1,000, South Korean media say. Most are in the northeast, and many help defectors flee North Korea and travel to third countries, including the South.

THAAD’s radar is capable of penetrating Chinese territory. Beijing has objected to the planned deployment, saying it will destabilize the regional balance of security, threaten China’s security and do nothing to ease tension on the Korean peninsula.

Many South Koreans believe Beijing is retaliating against THAAD, with measures against some companies and cancellations of performances by Korean artists.

On Wednesday, South Korea’s Lotte Group said Chinese authorities had halted construction at a multi-billion dollar real estate project after a fire inspection.