TAIPEI (Reuters) - Taiwan has lodged a protest against Cambodia’s decision to send suspects in a telecoms fraud scheme, including seven Taiwan nationals, to China for investigation, the self-ruled island’s foreign ministry said on Thursday.

Cambodia is one of China’s closest allies in Southeast Asia and does not recognize the government of Taiwan, which Beijing considers a wayward province.

It sent four Taiwanese suspects to China on Wednesday night, Taiwan foreign ministry spokeswoman Eleanor Wang told a regular media briefing on Thursday. Another three remain in Cambodia,

Taiwan “expresses solemn concerns and deep regrets about its Taiwan nationals being sent to China”, Wang said.

She said Taiwan had called on Cambodia to “truly guarantee our nationals’ judicial rights and interests and access to assistance” and for the Taiwanese suspects to be sent back to Taiwan for investigation.

The ministry said last week there were seven Taiwanese nationals among a total of 31 suspects.

Cambodia’s head of police investigation, Uk Heisela, told Reuters in Phnom Penh that a group of 17 suspects were sent to China on Wednesday and another group of 14 would be sent on Saturday.

“There is no Taiwanese national, they are all Chinese,” he said on Thursday. “When we detained them, they didn’t have any documents, China provided them with Chinese passports.”

Speaking in Beijing, Chinese Foreign Ministry spokesman Lu Kang said China “highly appreciated” Cambodia’s cooperation on fighting cross-border crimes involving fraud.

“On this issue, both countries have always maintained close communication and cooperation,” Lu told a daily news briefing.

Cambodia deported 13 people from Taiwan to China, where they were wanted on suspicion of telecoms fraud, last year despite opposition from Taipei, which accused Beijing of “abducting” its citizens.

China has never renounced the use of force to bring Taiwan under its control. China’s Nationalists fled to the island after losing the Chinese civil war with the Communists in 1949.