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A South Sudanese rebel spokesman has been deported to South Sudan over a Facebook posting, a Kenyan official said Friday, while colleagues feared for his life and human rights workers and a relative said he was a registered refugee with a U.S. green card.

Human rights groups immediately condemned Kenya's deportation of James Gatdet Dak, calling it a breach of international law.

"He became an inadmissible person, so we cancelled his visa and he was taken to his country of origin," Kenyan government spokesman Eric Kiraithe told The Associated Press. A police official said Gatdet was deported Thursday evening. The official spoke on condition of anonymity because he was not authorized to give the information.

Rebel leader Riek Machar pleaded with Kenya's deputy president not to deport Gatdet "due to profound fear for his life," Machar said in a statement. He said he told Kenyan officials that Gatdet was a refugee, and said the U.N. refugee agency "made serious efforts" to reverse Kenya's decision. He did not give details.

Fighting continues in South Sudan amid ethnic tensions, despite a fragile peace deal to end civil war.

The deportation came during a bitter dispute between Kenya and the United Nations over the U.N. secretary-general's firing of the Kenyan commander of the peacekeeping mission in South Sudan. The U.N. forces were accused of responding poorly to attacks on civilians in July.

The Facebook posting by Gatdet, a spokesman for Machar, supported the Kenyan commander's firing.

Kenya has responded angrily to the firing, noting that Lt. Gen. Johnson Mogoa Kimani Ondieki had been on the job for just three weeks when the July attacks occurred. Kenya has announced it is pulling its 1,000 peacekeepers from South Sudan and withdrawing from its peace process, in which it has played a key role.

Human rights workers said the deportation of Gatdet was going too far, saying Kenya violated international law by deporting a registered refugee. Documents seen by the AP indicate that Gatdet was registered in Kenya as a refugee in August 2015.

"On top of this, he is now at risk of arbitrary detention and torture in the hands of South Sudanese government authorities," Elizabeth Deng, a South Sudan researcher at Amnesty International, told the AP.

"In colluding with South Sudan and deporting James Gatdet Dak, Kenya has exposed him to a serious risk of persecution," said Gerry Simpson, senior refugee researcher at Human Rights Watch. "Kenya is steadily shredding any pretense of respect for its fundamental refugee protection obligations."

According to a family member of Gatdet who insisted on anonymity because they feared retribution from Kenya's government, he was arrested by South Sudanese national security officials when he landed in the capital, Juba.

"They tried to forcefully take (Gatdet) to the plane, and he struggled and refused to go, and the pilot refused to take him," the family member said of his departure from Kenya. "I am very much concerned. In the first place, I don't see a reason why he should be deported. He should have been taken to a different country."

Gatdet has a United States green card, the family member said.

In Geneva, U.N. refugee agency spokeswoman Cecile Pouilly said she was checking into what efforts the agency had made in Gatdet's case: "We are still trying to clarify a number of circumstances around this deportation."

She added: "The key element is that this person needs to have his rights protected and his well-being ensured by the government."

Gatdet might have dual nationality, Pouilly said, without giving details.

South Sudan, the world's youngest country, has been riven by ethnic violence since shortly after gaining its independence from Sudan in 2011. Civil war broke out in 2013 when government forces loyal to President Salva Kiir battled rebels led by his former vice president, Machar. Tens of thousands have been killed and more than 2 million displaced.

In three days of fighting in South Sudan's capital in July, at least 73 people were killed, including more than 20 internally displaced people who had sought U.N. protection, said a U.N. report released Tuesday. The report said "a lack of leadership on the part of key senior mission personnel culminated in a chaotic and ineffective response to the violence." The firing of the Kenyan commander was announced shortly afterward.

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Lynch reported from Juba, South Sudan. Associated Press writer Jamey Keaten in Geneva contributed.