A South Korean human rights activist who has accused Chinese security agents of torture during his four-month arrest said Thursday he will prove his claims through a medical checkup amid Beijing's denial of the alleged abuse.

The dramatic story of Kim Young-hwan, who was expelled from China and returned home on July 20, has taken another turn in recent weeks following his revelations of torture under Chinese detention.

The 49-year-old activist recently described the beatings, electric shocks and sleep deprivation he endured during the early days of his arrest in northeastern China, exposing the Seoul government to criticism about its lack of action against Beijing.

Kim was arrested on March 29 on suspicion of endangering China's national security, a charge believed to be related to the activist's efforts to help North Korean defectors in China and promote human rights in the North.

China's foreign ministry has rejected the allegations of torture, saying the investigation went according to law.

"Externally, there doesn't seem to be any scars remaining," Kim told Yonhap News Agency in a phone call. "I plan to get a medical checkup."

Formal evidence of the alleged torture is expected to help Kim in the event that he decides to sue the Chinese government or take the case to the United Nations.

Lee Kyu-ho, a 41-year-old Korean-Chinese, said he moved to South Korea in 2010 after having worked as a Chinese security agent from 1995 to 2002, and witnessed similar violence by Chinese authorities at the time.

"In 1996, we took into custody a male North Korean defector who appeared to be in his late 30s or early 40s, and during the investigation, I kicked him with my heels and beat him with an electric rod," Lee said in an interview with Yonhap.

"I was infuriated when I heard about the torture Chinese authorities used against Kim Young-hwan and decided to blow the whistle out of guilt about my past actions."

Kim's detention drew public attention due to his personal background.

He is a former South Korean proponent of North Korea's guiding "juche" philosophy of self-reliance who later renounced his pro-North Korean ideology and became active in projects to raise awareness about the North's dismal human rights record.

(Yonhap News)