By Aaron Maasho
ADDIS ABABA (Reuters) - Ethiopia defended its detention of an opposition leader with British citizenship on Friday and said he was being treated well, after London said the case risked hurting ties.
Andargachew Tsige was sentenced to death in absentia in 2009 over his involvement with an Ethiopian opposition organization, then arrested in Yemen five years later and extradited to Ethiopia.
Britain, a major donor with long historical ties to the Horn of Africa nation, said on Thursday Addis Ababa had failed to let its diplomats visit Andargachew regularly despite promises.
British foreign minister Philip Hammond said Andargachew remained in solitary confinement "without a legal process to challenge his detention," and the lack of progress in arranging access risked undermining relations.
Getachew Reda, an adviser to Ethiopia's prime minister, told Reuters on Friday officials had been cooperating with Britain, which was aware of Andargachew's condition.
"The grim stories some are trying to paint are absolutely groundless ... We do not want to let this stand in the way of our relations," Getachew said.
"But if the unconditional release of a convicted terrorist is what our British partners ask of us as a condition for maintaining our productive cooperation, it would simply be unfortunate," Getachew added. "It is our belief that they understand this."
Andargachew is secretary-general of Ginbot 7, which describes itself as a reform movement but is branded a terrorist group bent on overthrowing the government by Addis Ababa.
Rights groups have regularly accused Ethiopia, one of Africa's fastest-growing economies, of arresting journalists, activists and bloggers to stamp out dissent - allegations dismissed by the government.
Britain summoned Ethiopia's chargé d'affaires in August last year to seek assurances that Andargachew would not be put to death.
Ethiopia last carried out an execution in 2007, a rare move against a military officer convicted of killing a former head of security and immigration.
Ginbot 7 is among five groups Addis Ababa has blacklisted under anti-terror legislation, alongside the Oromo Liberation Front and the Ogaden National Liberation Front separatist groups, al Qaeda and Somalia's al Shabaab militants.
(Editing by George Obulutsa and Andrew Heavens)