Jerusalem (AFP) - His long beard, dangling sidelocks and wide smile give him the look of a hippie from another era, but Meir Ettinger has become the symbol of a crackdown on Jewish extremism.

The young man, whose grandfather headed a racist movement, was arrested on Monday, the first alleged extremist to be taken into custody in connection with Israeli Prime Minister Benjamin Netanyahu’s pledge of "zero tolerance".

The push to crack down on Jewish extremism follows the July 31 firebombing of a Palestinian home in the West Bank that killed an 18-month-old child and critically wounded his parents and four-year-old brother.

It came only hours after a stabbing attack at a Gay Pride parade in Jerusalem that wounded five people and killed a 16-year-old girl.

The incidents were unrelated, with the suspect in the Gay Pride stabbings an ultra-Orthodox Jew carrying out a "lone wolf"-type attack.

The firebombing however follows a pattern of such actions by suspected Jewish extremists against Palestinians, Christians and even the Israeli military.

Ettinger, 23 and from Jerusalem, is accused of being a key figure in an amorphous band of youths who have engaged in such violence.

After the torching of part of a shrine in northern Israel in June where Christians believe Jesus performed the miracle of loaves and fishes, the Shin Bet internal security agency labelled him the head of an "ideological infrastructure" responsible for the arson.

According to the Shin Bet, the same "infrastructure" vandalised a monastery in 2014 and unsuccessfully sought to disrupt Pope Benedict's visit the same year.

Ettinger's family is no stranger to controversy.

His grandfather Meir Kahane founded Kach, a racist movement that wanted to chase Arabs from Israel and which was banned in 1988.

Kahane was assassinated in New York in 1990.

His father is a rabbi at two religious schools in Jerusalem. His parents disapproved of his radical stance, and when he was 17, Ettinger left to live in the Israeli-occupied West Bank.

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- Hilltop Youths -

A number of illegal Jewish outposts have sprung up in the mountains of the West Bank on land Palestinians view as part of a future state of their own.

All Israeli settlements in the West Bank are considered illegal under international law. Israel grants approvals for settlements, but unauthorised outposts are also illegal under its laws.

Ettinger wandered from one outpost to another, allegedly becoming part of what is known as the "Hilltop Youth," a loose band of militants who left their schools and families to live in what they see as "Judea and Samaria" -- the name given to the West Bank in reference to the ancient Biblical kingdoms.

They advocate for the return of the ancient kingdoms where Jews can live under the laws of the Torah.

In his blog on July 30, Ettinger wrote of God's honour being "desecrated by idolatry filling the Holy Land".

He lashed out at "the state of Israel's great sin of allowing idolatry -- churches and monasteries abounding in the Land of Israel with the sound of their ringing bells mixing with the pleasant sound of the Torah and prayer that, thank God, is plentiful in the Holy Land."

Ettinger said "there are many, many Jews, much more than what people think ... who are committed not to the broken laws of the state but much more eternal laws, true and from a pure source."

His lawyer said Ettinger has never committed violence and called his arrest "window dressing".

For some, Ettinger was inspired by Yitzchak Ginsburgh, a rabbi from a messianic branch of Hasidic Judaism that denies Arabs the right to live in the Holy Land.

Ettinger spoke of him in January 2014 with a group of settlers who sought to destroy an olive grove in the Palestinian village of Kusra in the West Bank.

They were beaten by residents before being turned over to Israeli soldiers.

He is also reported to have broken into Joseph's tomb in Nablus despite restrictions imposed on Jews and to have collected information on authorities' plans to evacuate illegal outposts.

His alleged activities earned him six months in prison and a ban on travel to the West Bank and Jerusalem for one year. He was living in Safed in northern Israel for several months when he was arrested this week.