TAIPEI (Reuters) - Taiwan prosecutors angered China over the weekend by freeing 20 Taiwanese suspected of defrauding Chinese nationals in a telecoms scam but on Thursday changed their minds, taking most of them into custody on suspicion of committing “serious crime”.

The move came as island officials are in Beijing this week to negotiate the return of 45 of its citizens who were forcibly sent to China from Kenya and linked to a similar telephone fraud case abroad against Chinese nationals.

Taiwan at the time accused China of kidnapping the suspects.

China has since the end of the Chinese civil war in 1949 regarded self-ruled Taiwan as a breakaway province, to be taken back by force if necessary should it make moves towards independence.

Since Tsai Ing-wen and her independence-leaning Democratic Progressive Party won Taiwan’s presidential and parliamentary elections by a landslide in January, Beijing has been stepping up pressure on the self-ruled island.

Taiwan authorities had said they had requested evidence from China ahead of the arrival of the 20 Taiwanese deported on Friday from Malaysia, but no information was provided.

Hong Chia-juan, a chief prosecutor in the Taichung District Prosecutors Office, said Thursday’s move came after visual evidence gathered from Malaysian authorities gave his team the evidence they needed to detain most of the individuals for at least two months for investigation.

Two of the suspects were under effective house arrest with their movements limited, Hong said.

Led by the island’s justice ministry, Taiwan officials left for China on Wednesday in the hope of establishing a way to jointly investigate the two cases.