Supporters of a British man on hunger strike in a Greek jail say the prison authorities are refusing to move him to a hospital outside for treatment.
Briton Simon Chapman says evidence was planted on him
And the human rights group Amnesty International has expressed concern about his arrest and treatment.
Simon Chapman, 30, from Basildon, Essex, has not eaten since early October in protest at his arrest during a anti-capitalist march at the European Union summit in Thessaloniki.
Police in Greece have charged Mr Chapman with possessing Molotov cocktails, an axe and a hammer at the march which took place in June.
But he claims the items were planted on him and that he has video evidence to prove his innocence.
Call for 'independent investigation'
Simon Chapman, and three fellow prisoners - two Spaniards and one Syrian - have said they were subjected to violence by police and by prison officers during their initial detention period.
A spokesman for Amnesty International said: "We urge the Greek authorities to undertake a thorough, independent and impartial investigation into allegations of ill-treatment made by the demonstrators.
"Should the allegations be substantiated, we want to ensure that victims
receive adequate compensation and that the perpetrators of human rights
violations be brought to justice."
Despite his claims, Mr Chapman, along with the six other protesters, began hunger strike several weeks ago.
His supporters say he is now in a "critical" condition and the Greek authorities are still refusing to move him from a prison hospital into the public health sector.
Sara Ayech, from the Thessaloniki Prisoners' Solidarity Campaign, said: "From what I understand he is suffering from respiratory problems and liver problems and his doctors have asked for him to be transferred to a civilian hospital, but the request has been turned down."
The campaign claims Mr Chapman needs to be moved to a civilian hospital to improve his care.
He and four other hunger strikers are being treated in the high-security Korydallos prison hospital.