A South Sudanese activist is being held in Kenya and is facing deportation to his home country where he has received death threats and could be arrested, Human Rights Watch said Wednesday.

Prominent lawyer Dong Samuel Luak, who fled to Kenya in August 2013 after receiving death threats for defending a high-ranking politician accused of treason, was detained on Monday according to the US-based rights body.

HRW said Luak had been denied access to legal counsel and was subject to a deportation order.

Kenyan officials did not immediately respond to requests for comment.

"Dong Samuel Luak has been a vocal advocate for human rights in South Sudan for many years, and could face serious mistreatment if returned to South Sudan," said Leslie Lefkow, HRW's deputy Africa director, in a statement.

The rights group said Luak -- who has publicly criticised human rights abuses and corruption by South Sudanese government officials -- was brutally attacked at his home in Nairobi in October 2015.

HRW noted that in recent years Kenya had "unlawfully deported several prominent opposition members from neighboring countries to their countries of origin, despite being recognised as refugees under Kenyan law."

These include James Gatdet Dak, the main spokesman for exiled opposition leader Riek Machar, who was deported in November 2016 and arrested upon his arrival in Juba. He has been held without charge ever since, according to HRW.

The world's youngest nation, South Sudan descended into war in December 2013, two years after achieving independence, leaving tens of thousands dead and more than 3.1 million people displaced.