Taiwanese activists who say they were were detained by Singapore authorities ahead of the landmark meeting between President Ma Ying-jeou and Chinese leader Xi Jinping slammed their treatment as "unacceptable" Sunday.
Their comments came as protests broke out again overnight in Taipei over the summit, the first time leaders from both sides of the strait have met since their split in 1949, a move seen by Ma's opponents as selling out to China.
Police in Singapore -- a city state where public protests are banned -- said Saturday they were interviewing five Taiwanese nationals amid a security clampdown at the summit venue.
Three members of anti-China political party Taiwan Solidarity Union (TSU) were taken away from a Singapore hostel for police questioning Saturday morning and were released later that night, a spokesman in Taipei said.
TSU legislative candidate Hsiao Ya-tan was one of those detained, spokesman Liu Ching-wen added, saying they had briefly been able to communicate with her while she was being questioned.
"If they were indeed taken away from the hostel where they were staying, that would be unacceptable," another TSU spokesperson, Chow Mei-li, told AFP.
"How could police arbitrarily enter and take away foreigners when they did nothing that broke their laws?" she added.
It is not clear what the activists were questioned over by Singapore police.
The three are expected to arrive back in Taipei Sunday afternoon.
Separately, three youth activists who had traveled to Singapore on Saturday but had not been allowed through immigration were deported back to Taipei Sunday morning.
They had planned to hand a letter to Taiwan's representative office in Singapore and were out of contact for more than 10 hours, according to Democracy Tautin, one of the social movement groups involved.
"The intentions and actions to peacefully petition are entirely legitimate, reasonable, lawful, and don't infringe on anyone's rights," the group said in a Facebook post.
When asked why they were not allowed through immigration, Singaporean authorities replied: "That's the particular rule for today," according to Democracy Tautin.
Supporters of a pro-unification group chanted slogans while a smaller group of TSU members scuffled briefly with police at Taipei's Taoyuan Airport overnight as Ma arrived home.
Hundreds had gathered in the capital Saturday to condemn the summit.
China-Taiwan relations have warmed under Ma's administration, but he has seen his popular support plummet as the public become increasingly fearful of greater Chinese influence on the democratic island.