Amnesty - Israel must release a Palestinian activist held without charge for two years, Amnesty International urged after his administrative detention was extended for the sixth time without justification.

Ahmed Qatamesh, a 62-year-old academic who Amnesty International believes is being detained to deter political activities by other Palestinian left-wing activists, was told he will be held for at least another four months from 29 April.

"Ahmed Qatamesh is a prisoner of conscience who is being detained solely for expressing non-violent political beliefs," said Amnesty International's Ann Harrison, Deputy Director of the Middle East and North Africa Programme.

"His continued detention is arbitrary and he must be immediately and unconditionally released."

Ahmad Qatamesh is one of about 160 Palestinians currently held by Israel under administrative detention orders.

These allow for indefinite detention on the basis of secret evidence that the military prosecution withholds from the detainee and their lawyer, denying detainees the basic right to defend themselves.

"The cruel nature of administrative detention means detainees and their families live in a constant state of uncertainty. As each order expires their hopes are raised and then dashed as they are handed a fresh order," said Ann Harrison.

Ahmad Qatamesh's wife, a board member of local NGO Addameer, told Amnesty International this week that it "would have been easier" for the family if her husband had been sentenced to three years’ imprisonment.

Ahmad Qatamesh is a political writer who has called for a one state solution to the Israeli-Palestinian conflict.

There is no apparent reason to hold him, and since his arrest he has not been charged or brought to trial.

Ahmad Qatamesh's ordeal began on 21 April 2011 when he was arrested from his brother’s house in Ramallah by Israeli security forces.

His daughter said security forces ordered her at gunpoint to telephone him after they failed to find him at his own home.

Since then, Qatamesh has been questioned for a mere 10 minutes by the Israel Security Agency (ISA).

They claim that he is a member of the political wing of the Popular Front for the Liberation of Palestine (PFLP) and poses a security threat.

He says he has not been involved with PFLP for 14 years, although in the 1990s he was a political and intellectual supporter.

“I am under arrest now and don't know why," he said in June 2011.

Palestinians in the occupied West Bank face huge obstacles in obtaining permits to visit relatives in detention even though the Geneva Convention stipulates that individuals under occupation should be held within the occupied territory.

Ahmad Qatamesh’s wife says he has suffered from undiagnosed ailments causing nausea and faintness – but his request to see an independent doctor has been refused by prison authorities.

"The Israeli government must stop the use of administrative detention and release all administrative detainees unless they are promptly charged with internationally recognizable offences and tried in accordance with international fair trial standards," said Ann Harrison.

Ahmad Qatamesh was held without charge for over five years in the 1990s. After his release in 1998, he wrote about his experiences – including being subjected to torture – in a book entitled I Shall Not Wear Your Tarboosh.