Seoul, South Korea (CNN) On Saturday, Kim Mi-ok waited in a Chinese border city for her husband to step off the train from North Korea.

He never emerged.

"I waited until the last passenger. I waited until the train doors closed, but I couldn't find him," Kim said.

The next day, North Korea's state news agency announced security services had detained Kim's husband, Kim Hak-song , "on suspicion of hostile acts against the state."

"I was speechless, I was in shock," his wife said, speaking to CNN in an emotional interview.

Kim Hak-song, left, and his wife, Kim Mi-ok, in a photo provided to CNN by the family.

Weeping and beating her chest, she said her husband had been falsely accused.

"He went to the country and served with love and I believe his words that there was nothing else," she said.

Kim Hak-song is an ethnic Korean who was born in China. He became a naturalized US citizen more than a decade ago. It was there that he was also ordained as an evangelical Christian pastor affiliated with the Oriental Mission Church in Los Angeles.

Kim's wife said her husband had been teaching agricultural techniques at Pyongyang University for Science and Technology. She insisted that he did not engage in missionary work in fiercely atheistic North Korea.

Kim's wife, left, and Kim, center, in a photograph with other family members.

"He worked as a farmer," Kim's wife said. "He always loved the soil and the land."

She showed CNN photos of her smiling husband standing in rice paddies at an experimental farm where he worked on the outskirts of Pyongyang.

"Last year they had a big harvest," she said.

In the 1990s, North Korea suffered from a famine that was estimated to have led to the deaths of some 2.5 million people.

Kim says she and her husband made multiple trips to North Korea in recent years in connection with the university.

The first signs of trouble came on April 22, when the North Koreans suddenly detained Tony Kim, a fellow Korean-American academic teaching at the same university in Pyongyang.

On Friday, North Korean officials announced the launch of a campaign to root out suspected foreign agents, after Pyongyang made dramatic, unsubstantiated claims to have foiled a CIA-backed plot to assassinate supreme leader Kim Jong Un.

US and South Korean intelligence officials have dismissed the accusations.

Now, with the detention of the second Korean-American working at Pyongyang University in barely two weeks, a tearful Kim Mi-ok had a message for the North Korean government.

"We are all the same people," she said. "I hope this detention is solved in a humanitarian way and he is sent back to our family. Our family members are waiting."