Cambodia deported 25 Taiwanese nationals wanted on fraud charges to China Friday, a police officer said, despite vehement opposition from Taipei which wanted the suspects returned to Taiwan.
Taipei accuses Beijing of "abducting" its citizens from countries that do not recognise the island's government — such as close China ally Cambodia.
"The Chinese plane just took off from the Phnom Penh airport with the suspects," Cambodian immigration officer Uk Heisela told AFP.
He added that the 25 Taiwanese suspects were joined by 14 Chinese nationals, all of whom were recently arrested for allegedly running a telephone fraud scam targeting victims on the mainland.
"Chinese police came with the plane. Each suspect was escorted by two Chinese police," he added.
Taiwan's foreign ministry slammed the move Friday and said Cambodia went ahead with the deportation "despite strong demand from our side".
"The foreign ministry expresses its strong dissatisfaction about the handling and has instructed our representative office in Ho Chi Minh city to express our serious concerns and deep regrets to the Cambodian side," it said in a statement.
It added that Cambodia faces significant pressure from Beijing to uphold its 'one China' policy.
A foreign ministry spokeswoman said Taiwan was only aware of 18 nationals on board the plane, though Cambodian police insist the number is 25, including ten who were not carrying passports.
China considers Taiwan to be one of its provinces awaiting reunification, by force if necessary, even though the island has ruled itself since 1949 following a civil war split.
Taiwan insists citizens deported from third countries should be returned to the island and not to mainland China.
But Cambodia, one of Beijing's closest allies in Southeast Asia, refuses to differentiate between China and Taiwan, simply referring to nationals from the latter as "island Chinese".
In April Malaysia and Kenya also sparked uproar in Taipei when they returned Taiwanese nationals accused of crimes to mainland China.
Observers saw the deportation cases as Beijing's effort to pressure the new Taiwanese government that took office in May.
China does not trust the traditionally pro-independence ruling Democratic Progressive Party (DPP).
Taiwan's new president Tsai Ing-wen has repeatedly pledged to maintain the "status quo", but she also has not bowed to pressure to accept Beijing's definition of cross-strait relations.