Amnesty International has accused the Israeli authorities of subjecting jailed nuclear whistleblower Mordechai Vanunu to cruel, inhuman or degrading treatment by holding him in solitary confinement.
The 56-year-old, who spent 18 years in prison for revealing details of the country's nuclear arsenal to a UK newspaper in 1986, was sent back to jail for three months on 23 May on charges of contact with a foreign national, and almost immediately placed in solitary confinement.
Amnesty International has called for his immediate and unconditional release.
"Mordechai Vanunu should not be in prison at all, let alone be held in solitary confinement in a unit intended for violent criminals," said Malcolm Smart, Director of Amnesty International's Middle East Programme.
"He suffered immensely when he was held in solitary confinement for 11 years after his imprisonment in 1986 and to return him to such conditions now is nothing less than cruel, inhuman or degrading."
Vanunu is held in Ayalon Prison in central Israel. His lawyer revealed to Amnesty International that he has been placed in an isolated cell, ostensibly to protect him from other prisoners.
For years, Vanunu has been portrayed by some Israeli media and politicians as a traitor and an enemy of the state for disclosing Israeli efforts to develop nuclear weapons, and he says he has received death threats.
"Mordechai Vanunu is a prisoner of conscience. The prison authorities might claim that he has been put in isolation to protect him from the risk of attack by other inmates, but if the Israeli government is really concerned for his safety it should release him without delay," said Malcolm Smart. "His re-imprisonment is both harsh and unjustified."
Vanunu, a former technician at Israel's nuclear plant near the southern town of Dimona, revealed details of the country's nuclear arsenal to UK newspaper The Sunday Times.
Subsequently, he was abducted by Mossad agents in Italy on 30 September 1986 and secretly taken to Israel, where he was tried and sentenced to a prison term of 18 years, the first 11 years of which he spent in solitary confinement.
Since his release in 2004, the Israeli authorities have subjected Vanunu to police supervision under the terms of a draconian military order, which is renewed every six months.
According to the order, he is banned from communicating with foreigners, including journalists. He cannot leave the country and is forbidden from approaching foreign embassies. He must also inform the authorities if he wishes to change his address.
"The restrictions on Mordechai Vanunu arbitrarily limit his rights to freedom of movement, expression and association and are therefore in breach of international law. They should be lifted and he should be allowed to start his life again as a free man," said Malcolm Smart.
Mordechai Vanunu's brother, Meir Vanunu, told Amnesty International on 17 June: "It is very traumatic for Mordechai to be put again in solitary confinement and subjected to harassment. These are the same conditions he was kept under previously for 18 years and there is no justification for it after 24 years of suffering.
"We fear for the impact this will have on his health. Now is the time for Mordechai's true freedom – he should be allowed to travel and leave Israel. He should never have been put in this situation in the first place."
The harsh conditions of the dangerous criminals unit in Ayalon Prison mean Vanunu can only leave his cell for one hour every day to walk in the prison courtyard.
He cannot currently make telephone calls from the prison unless he submits information about the person he wishes to call to the prison authorities – something he refuses to do on principle. As a result, he has had no contact with friends or family since the beginning of his current imprisonment.
His lawyer Michael Sfard was able to visit him and told Amnesty International: "Mordechai Vanunu is suffering from isolation. He should not be made to pay a price because of the enmity of others towards him."