Nairobi - An Ethiopian opposition leader with British citizenship faces the death sentence after being extradited to Addis Ababa, Human Rights Watch said on Monday, urging the government to ensure his safety.
HRW said Andargachew Tsige, the secretary general of the outlawed Ginbot 7 group, had been "unlawfully deported by Yemen" back to Ethiopia.
"Yemen blatantly violated its international legal obligations by deporting someone to Ethiopia who not only is at serious risk of torture, but also faces the death sentence after being tried in absentia," HRW deputy Africa director Leslie Lefkow said.
Ethiopia has not said where Andargachew is, but his supporters and HRW - quoting "credible sources" - said he is in Ethiopian custody.
Andargachew, an Ethiopian-born British citizen, was arrested in June while transiting through Yemen's Sana'a airport to Eritrea, according to a statement from Ginbot 7.
According to HRW, Andargachew faces the death sentence from convictions in two separate trials in absentia in 2009 and 2012.
An Ethiopian government spokesman last week said Andargachew was a "criminal" who will "have his day in court."
"Ethiopia needs to demonstrate that it is holding Andargachew in accordance with its international obligations, and he should be allowed immediate access to a lawyer, his family, and to British consular officials," Lefkow added.
Britain's Foreign Office said last week that it was investigating reports Andargachew was in Ethiopia and said it had "deep concerns" about the case.
The US-based Ginbot 7 is considered a terrorist organisation under Ethiopian law, and in 2012 several people were convicted for having links to the group, including journalist Eskinder Nega.
The party - founded by Addis Ababa's former mayor, Berhanu Nega - says it is fighting for democracy in Ethiopia and calls for the violent overthrow of the ruling party.
Its name commemorated the Ethiopian calendar date - 15 May in the Gregorian calendar - when post-election violence in 2005 left over 200 people dead.
Several people were convicted under Ethiopia's anti-terrorism legislation in 2012 for having links to the group, including journalist Eskinder Nega and opposition leader Andualem Arage.