China has again denied allegations that it tortured a South Korean human rights activist during his four-month arrest, Seoul's foreign ministry said, indicating growing diplomatic tensions over the issue.

The denial was Beijing's first official response to Seoul's request for a reinvestigation into claims by activist Kim Young-hwan that he was tortured by Chinese security agents during the early days of his arrest in northeastern China.

"China treated (Kim) in a civilized and humanitarian manner according to relevant legal processes while respecting his legitimate rights," the ministry quoted Chinese Assistant Foreign Minister Zhang Ming as saying during a meeting with South Korean Ambassador to Beijing Lee Kyu-hyung on Friday.

Zhang also said Kim was "treated favorably from the broad perspective of friendly South Korea-China relations," the ministry said in a press release issued late Friday.

Presenting Kim's detailed testimony, Lee urged the Chinese government to conduct another thorough probe into the case and take follow-up measures, including an apology, punishment for those responsible and efforts to prevent a recurrence of the alleged torture, the ministry said.

The dramatic story of Kim, who was expelled from China and returned home on July 20, took another turn in recent weeks following his revelations of torture under Chinese detention. The 49-year-old activist has described beatings, electric shocks and sleep deprivation, 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 has consistently rejected the allegations of torture, saying the investigation went according to law.

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.