Kenya acquitted a group of Taiwanese citizens in a cybercrime case last week, and then deported them to China. Taiwan says the forced departure constitutes an "abuction" of its citizens by Chinese authorities.
The eight Taiwanese nationals were among 77 ethnic Chinese arrested by Kenyan authorities in November 2014 accused of illegally entering the country and being involved in a telecoms scam. They were among a first group of suspects who were found not guilty by a Kenyan court last Tuesday.
However, eight of them were deported to China by Kenyan authorities due to Chinese pressure, the Taiwanese Foreign Ministry said in a statement on Monday.
"This is an uncivilized act of illegal kidnapping and a serious violation of basic human rights," it added, demanding the immediate return of the eight.
Taiwan has no diplomatic ties with Kenya, which only recognizes the government in Beijing. Its nearest diplomat is based in the South African capital.
The statement added that news of the court's verdict had been delayed by China's "technical methods" and "by the time our official rushed to the airport, the eight Taiwan citizens had been forcefully taken."
They were forced to board a China Southern Airlines plane to the mainland, it said.
New strain on relations
China still regards Taiwan as part of its territory awaiting reunification, by force if necessary, even though Taiwan has ruled itself since 1949.
Ties between the two have rapidly improved in recent years but tensions have begun to rise again since Tsai Ing-wen and her independence-leaning DPP won presidential and parliamentary elections in January. Tsai is set to be inaugurated as president on May 20 amid warnings from Beijing against any moves towards formal independence.
On Monday, Chinese Foreign Ministry spokesman Lu Kang said he needed to "further understand" the situation, when asked about the whereabouts of the eight Taiwanese in a media briefing.
Kenyan government officials were not immediately available for comment.