The international rights watchdog Amnesty International has called on Israel to immediately release a Palestinian writer who has been jailed without charges or trial.

Israeli forces arrested 66-year-old Ahmad Qatamesh on May 14 during house raids across the occupied West Bank and East Jerusalem.

Last week, he was placed under a three-month period of administrative detention, a practice in which Israel imprisons Palestinians without charge or trial, often based on "secret evidence". An Israeli military court has yet to approve that order.

In a statement released on Wednesday, Magdalena Mughrabi, Amnesty's deputy director for the Middle East and North Africa, called Qatamesh a "prisoner of conscience".

The group said he was "detained solely due to his non-violent political activities and writing and to deter activism by other Palestinians".

Qatamesh is an influential author, writer and professor whose lectures are widely attended in the West Bank. He is well known for his solidarity activism on behalf of Palestinian prisoners in Israeli jail.

"Ahmad Qatamesh shouldn't spend a single minute more behind bars, let alone be detained for three months without charge or trial," Mughrabi said.

"He is a prisoner of conscience and should be released immediately and unconditionally."

In the statement, Mughrabi also called for Israel to end its "cruel" use of administrative detention altogether.

"Instead of indefinitely detaining Palestinians without charge or trial, Israel should end its use of administrative detention, which inflicts huge emotional suffering on detainees and their families, placing them in a permanent state of uncertainty," she said.

At time of publication, the spokesperson for the Shin Bet, the Israeli intelligence agency, had not replied to Al Jazeera's request for a comment.

READ MORE: Israel jails writer Ahmad Qatamesh without charges

According to The Times of Israel, the Shin Bet has accused Qatamesh of membership in the leftist Popular Front for the Liberation of Palestine (PFLP).

Suha Barghouti, his wife, rejects those claims, believing instead that he was targeted for his vocal support of Palestinians on hunger strike in Israeli jails for the last 38 days.

The Palestinian Ma'an News Agency estimates that 1,300 Palestinians are currently fasting behind bars, while Israeli media outlets have put the number in the high hundreds.

Barghouti told Al Jazeera that Israeli intelligence has summoned her husband for interrogation several times in the past year, often warning him to not speak too provocatively in support of prisoners' rights and other struggles.

"He says he will go on for his life telling his opinion," she said earlier this week. "We don't know yet what is happening or why, but I think [it happened] because he is campaigning for the prisoners and is very active."

She added: "The Israelis believe targeting intellectuals and civil society is the most effective way."

Years behind bars

Qatamesh has been arrested by Israel time and again. Of the more than 13 years he was behind bars, at least eight and a half were under administrative detention.

He was first jailed in the 1970s for charges related to alleged involvement in the PFLP.

In 1992, Israel arrested him yet again and placed him under administrative detention for more than six years. In his book I Shall Not Wear Your Tarboush, Qatamesh wrote about torture and rights violations he says he endured during that period.

He was arrested yet again in April 2011 and placed under administrative detention for more than two-and-a-half years. In 2013, Amnesty International deemed him a "prisoner of conscience" while he was still behind bars and called for his release.

READ MORE: What it means to be a Palestinian prisoner in Israel

Alaa Tartir, programme director at Al-Shabaka: The Palestinian Policy Network, also believes that Israel targeted Qatamesh to quell solidarity with the ongoing mass hunger strike.

"As a brutal military occupation regime, [Israel] reacts violently [to the growing solidarity]," he told Al Jazeera by email, arguing that it is using protests for the hunger strike as a pretext to carry out yet more arrests.

"Qatamesh, a prisoner of conscience according to Amnesty International, was targeted by Israel in an attempt to silence such voices and limit their public influence."

Of the more than 6,300-plus Palestinians in Israeli jails, an estimated 500 are administrative detainees, according to Addameer, a West Bank-based prisoners' rights group.