Cambodia deported 25 Taiwanese nationals wanted on fraud charges to China Friday, an official said, prompting an angry rebuke 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.

Immigration officer Uk Heisela confirmed a Chinese plane left Phnom Penh "with the suspects" on Thursday morning.

"Chinese police came with the plane. Each suspect was escorted by two Chinese police," he said.

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.

Taiwan's foreign ministry slammed the move Friday and said Cambodia went ahead with the deportation "despite strong demand from our side".

It added that Cambodia faces significant pressure from Beijing to uphold its 'one China' policy.

The island's Mainland Affairs Council, which handles relations with Beijing, said it would "continue to negotiate with the Chinese side in the hope that those involved will be sent back to Taiwan for trial".

Taiwan is self-ruling after a civil war split with China in 1949, but Beijing still sees it as a part of its territory waiting to be reunified.

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".

China's foreign ministry spokeswoman Hua Chunying said China "appreciated" Cambodia dealing with the case on the basis of its "one China" principle.

"We will ensure the legitimate rights of the victims of the fraud cases," she added.

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.