SEOUL A South Korean rights activist released by China after nearly four months' detention accused Chinese authorities on Monday of torturing him and three colleagues for working with North Korean refugees and said North Korea was probably behind the ill-treatment.
Kim Young-hwan and three other activists were returned to the South in July after being held by China's state security for conspiring to harm China's national interests. Beijing has denied torturing them.
Kim, who has been a prominent human rights activist with extensive experience in China and with contacts in the North, also said Pyongyang's new leader, Kim Jong-un, had stepped up surveillance of officials and residents alike as part of a campaign to boost the stability of his regime.
The high-profile arrest of the Seoul-based activists and accusations of torture have caused friction between the Asian neighbours, which have active commercial ties but have had sharp differences on how to deal with North Korea.
North and South Korea are technically still at war after their 1950-53 civil conflict ended in a truce, not a peace treaty. China is North Korea's only major ally.
Kim said he and the others were arrested in March and tortured with electric shocks and deprived of sleep for refusing to answer questions about their work helping North Korean refugees.
"I was subjected to electric torture using electric rods, for five to eight hours," Kim told reporters. "We also received sleep deprivation torture for six straight days. I suspect this is a case initiated by the North's state security."
South Korea has complained to China and demanded an investigation.
Kim, who is known to work with an extensive underground movement inside the North near China's border, was sceptical about immediate reform.
The North's third generation of the ruling Kim dynasty led by the 20-something Kim Jong-un is believed to be planning to mend its broken economy.
"I have serious doubts about whether North Korea has the endurance to overcome the obstacles of undertaking reform and opening," Kim Young-hwan said.
He suggested any change, even if positive, would be preceded by traditional strong-arm tactics by the state.
"I believe there will be stronger oppression and surveillance to create the mood of acceptance for reform and opening and to prevent any negative fallout from such moves."
(Reporting by Jack Kim; Editing by Nick Macfie)