The Ramallah-based Addameer human rights group said Hasan Safadi, who has been held for a year under a procedure known as "administrative detention" that allows prisoners to be held indefinitely without charge or trial, had relaunched his hunger strike after his detention was renewed.
The group said he was immediately placed in solitary confinement in what it called "a blatant violation" of an agreement last month between the Israel Prison Service and 1,600 hunger-striking Palestinian prisoners.
A spokeswoman for the Israel Prison Service said she could not confirm the report, explaining that it takes a few days before it can be determined if a prisoner is actually on a hunger strike.
Under last month's deal, prisoners currently in administrative detention would either be formally charged or released at the end of their terms, which typically are about six months, both sides said at the time.
Safadi was arrested a year ago at his Nablus home and was immediately placed in administrative detention for six months, a term that was later renewed. He went on a hunger strike for 71 days demanding his release, but ended it after he received assurances that he would be released at the end of his second term.
Addameer accused the Israel Prison Service of not honoring the terms of its agreement with the prisoners because administrative detention has been renewed for about three dozen prisoners.
The IPS spokeswoman said it was made clear in the agreement that administrative detention would continue if there was justification.
Meanwhile, Mahmoud Sarsak, a member of the Palestinian national soccer team who has been held since 2009, ended his three-month hunger strike earlier this week after he was promised release July 10.
Photo: Palestinian women chant slogans and hold pictures of Mahmoud Sarsak, who has been held by the Israelis since 2009, during a protest June 11 outside the International Committee of the Red Cross building in Gaza City. Credit: Hatem Moussa / Associated Press