Meir Ettinger, the head of a Jewish extremist group, stands at the Israeli justice court in Nazareth Illit on August 4, 2015.

An Israeli court on Tuesday extended the detention without trial of a Jewish extremist suspected of attacks, after a request from the Shin Bet internal security agency, his lawyer said.

Meir Ettinger, a 23-year-old accused of being a key figure in a loose band of youths suspected of a string of nationalist hate crimes targeting Palestinians, Christians and even Israeli soldiers, has already been in administrative detention for seven months.

He was placed under the controversial measure in August, just days after a lethal firebomb attack on a Palestinian home in the West Bank which resulted in the death of a couple and their toddler.

Israel has charged two Jews over the attack but Ettinger has not been directly linked to the incident, which prompted a crackdown on Jewish extremists.

A number of Jews were arrested following the attack, but as of Tuesday only Ettinger is still in administrative detention after some were released and others charged, a legal group said.

A statement from Honenu, a legal organisation which defends right-wing Jewish extremists, said a District Court judge approved the Shin Bet’s request — also accepted by Defence Minister Moshe Yaalon — to extend Ettinger’s detention by four months.

Ettinger’s lawyer, Yuval Zemer, said the extended detention “just because of one’s opinions” marked “a sad day for democracy.”

“Today Ettinger’s opinions don’t have a pleasant ring to the regime’s ears, tomorrow it could be my opinions or those of any citizen,” he said in a statement relayed by Honenu.

Ettinger’s grandfather Meir Kahane founded Kach, a far-right movement that wanted to chase Arabs from Israel. Kahane was assassinated in New York in 1990.

Administrative detention is intended to allow authorities to hold suspects while continuing to gather evidence, with the aim of preventing further attacks in the meantime. It also allows authorities to avoid divulging sensitive intelligence in court proceedings.

Rights group B’Tselem said at the start of the year that Israel was holding 584 Palestinians under the controversial measure, including journalist Mohammed al-Qiq, who is three months into a hunger strike to protest his arrest.

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