By Prak Chan Thul

PHNOM PENH (Reuters) - Cambodia will deport 21 Taiwan nationals to China, a senior Cambodian official said on Monday, ignoring attempts by Taiwanese officials to have them returned instead to Taiwan.

Cambodia does not have official relations with self-ruled Taiwan and considers the island part of "one China", in line with Beijing which considers the island a breakaway province.

Cambodia detained the 21 Taiwanese along with 14 Chinese nationals in coordination with Chinese authorities who are attempting to halt the proliferation of internet and phone extortion scams that have cost billions of dollars and driven some victims to suicide.

Cambodia has deported more than 200 people suspected of involvement in the rings to China since November.

"We will deport them to China under the one-China policy," Uk Heisela, investigation chief at Cambodia's immigration department, told Reuters. "They have all confessed to committing the crime."

Taipei has accused Beijing of kidnapping when other countries such as Kenya and Malaysia have deported Taiwanese people to China.

Taiwan's attempts to have the suspects deported to Taiwan had failed, Taipei's foreign ministry said in a statement. Pressure from Beijing would likely lead to Cambodia deporting them all to China, the ministry said.

Taiwan officials based in Vietnam traveled to Cambodia but were not allowed to visit the Taiwanese suspects, the ministry added.

Heisela and Kem Sarin, spokesman for Cambodia's immigration department, said they were unaware of a visit by Taiwanese officials.

China is Cambodia's largest foreign investor, and Cambodia is one of Beijing's staunchest regional allies.

Cambodia had yet to set a date for the deportation, Heisela said. Cambodian authorities arrested 13 of the Taiwanese along with 14 Chinese nationals on June 13. Another 8 Taiwanese suspects were detained on Saturday, said Heisela.

Cambodian police said the suspects contacted people in China asking for money to free relatives held captive. The suspects had admitted to posing as police and court officials to extort money, Heisela said.

Human Rights Watch said Cambodia's close relationship with China had led it to ride roughshod over human rights.

"This group should be allowed to appeal their deportation in a full and fair hearing in a court of law rather than be hustled on to a plane and sent to an uncertain fate back in China," said Phil Robertson, the group's deputy director in Asia.

Since 2011, nearly 8,000 people have been arrested in countries including Indonesia, Cambodia and the Philippines on suspicion of involvement in similar fraud schemes.

(Additional reporting by J.R. Wu in TAIPEI; Editing by Simon Webb)