RAMALLAH (Ma'an) -- Israeli authorities continue to violate an agreement signed with prisoners on May 14 to end a mass hunger strike, detainees and rights groups say.

Dirar Abu Sisi is still being held in isolation despite Israel's pledge to end solitary confinement, detainees told prisoner society lawyer Loai Akka on Thursday.

Abu Sisi suffers from chronic illnesses, the lawyer said in a statement.

An engineer from Gaza, 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.

Meanwhile, Samer al-Barq, 38, relaunched his hunger strike after Israel renewed his administrative detention order on May 21.

Al-Barq joined the mass hunger strike on April 17, but ended the strike on May 14 along with around 2,000 other prisoners when Israel agreed to "facilitate" the detainees' demand to end its policy of detention without charge or trial.

He has been detained without charge since July 2010 and is now in Ramle prison clinic.

Amnesty International said Wednesday that Israel had renewed at least 30 administrative detention orders and issued at least three new ones since the deal.

"It is business as usual when it comes to detention without charge or trial," Deputy Middle East Director at Amnesty, Ann Harrison, said.

She added: "Family visits for Gazan prisoners have still not started."

Under the deal, Israel also agreed to allow residents of Gaza to visit their relatives in Israeli prisons for the first time since 2007.