The Central Committee of the DPRK Red Cross said it sent a letter to its South Korean counterpart which calls for Seoul to return the workers without condition.
Seoul said last week that the 13 North Koreans working at a restaurant in China have begun to settle down here after undergoing a months-long probe in the wake of their rare mass defection in April.
The North's Red Cross said that Seoul's announcement is "a mean plot" to avoid public criticism of forcible detention of its citizens and "cover up the truth behind the group abduction."
It is not the first time that North Korea has claimed that the defectors were kidnapped by South Korea's spy agency.
Related to high-profile defections, Thae Yong-ho, a senior North Korean diplomat based in London, also defected to South Korea recently, making him one of the highest North Korean officials to escape the repressive regime.
In its first official response to Thae's defection, North Korea's state media on Saturday called him a "human scum," claiming that he allegedly embezzled state funds, leaked state secrets in exchange of money and raped a minor. (Yonhap)