Foreign Minister Kim Sung-hwan pledged Thursday to make diplomatic efforts to press Beijing to swiftly release four South Korean activists who have been detained in China since late March.

The four activists, including Kim Young-hwan, a senior researcher for the Network for North Korean Democracy and Human Rights, a Seoul-based civic group for North Korean defectors, were arrested by Chinese police in the northeastern Chinese city of Dalian on March 29.

The detention drew media attention early this week after the civic group issued a press release demanding China free the detainees.

"The most important thing for now is to set them free as early as possible," the minister told a meeting at his office with the family of the Kim Young-hwan and members of the civic group.

"The government is making utmost efforts to resolve this issue," the minister said, adding South Korea has continued to consult with China on the issue.

Kim Young-hwan, 49, is a former South Korean proponent of North Korea's guiding "juche" philosophy of self-reliance. He met with the North's founding leader Kim Il-sung in 1991 after sneaking into the North via a North Korean submersible.

However, Kim Young-hwan later renounced his pro-North Korean ideology and became active in projects to raise awareness about the dismal human rights record in North Korea.

The four men were arrested on charges of endangering China's national security but no further details of their alleged crimes have bee disclosed, ministry officials said.

They are being held in the Chinese border city of Dandong across the Yalu River from North Korea.

Foreign ministry spokesman Cho Byung-jae said his ministry "contacted the relevant government authorities of China and requested the case be handled in a swift and fair manner."

"The ministry on May 10 requested the national stability agency in the Chinese province of Liaoning allow a meeting between Kim and a lawyer," Cho said. 

"In the case of the other three, who allegedly rejected consular access in writing, the ministry is making efforts to confirm that is their will," the spokesman said. (Yonhap News)