A Palestinian man held in solitary confinement by Israel for two years is losing his ability to recall language and has speech impairments, a lawyer who visited him in jail said Sunday.

The lawyer for the Palestinian prisoners society said Dirar Abu Sisi, an engineer from Gaza, is suffering from a number of health problems in his isolation cell.

Abu Sisi disappeared in February 2011 while traveling on a train in Ukraine and Israel later announced that it was holding him in a southern Israeli jail.

He was the only prisoner excluded from a May 2012 deal with Israeli authorities to end solitary confinement, according to prisoners rights group Addameer.

The deal, which included several terms to improve prisoners conditions, was made to end a mass hunger strike campaign launched by Palestinian prisoners.

The order to keep Abu Sisi in isolation was renewed for another six months on Nov. 1, 2012.

The prisoners society lawyer said Abu Sisi told him prison guards were implementing other punitive measures.

They bring him rotten food, and recently confiscated his notebook where he records his thoughts during his isolation, Abu Sisi said.

The technical director at Gaza's sole electricity plant, Abu Sisi was charged with developing Hamas' rocket capabilities. Abu Sisi denies the charges and Hamas says he has no affiliation to the group.

Disappearance

Abu Sisi, father of six and the husband of a Ukrainian woman, disappeared while traveling between Kiev and the eastern city of Kharkov on the night of Feb. 18-19.

His wife Veronica said train attendants told her that her husband had been taken away by two men posing as officers of the Ukrainian secret service. A month later, Israel partially lifted a gag order on reporting his disappearance and Abu Sisi turned up in Israeli court.

Secretive detentions in Israel have come under the spotlight in recent days, after an Australian TV report identified the mysterious 'Prisoner X' as Australian citizen Ben Zygier.

Zygier, a possible Mossad operative detained on suspicion of security offenses, was held in isolation and his identity shrouded in secrecy. He committed suicide in Israeli jail in 2010.