The failed arrest of an Israeli activist who campaigns to prevent Jews marrying Arabs has fuelled controversy over the far-right group he leads.

Ben Zion Gopstein, who founded the anti-miscegenation organisation Lehava, was arrested on Sunday along with other group members on the suspicion of threatening and encouraging attacks of Arab men who are in relationships with Jewish women.

But despite police objections, the Jerusalem District Court ordered them released 24 hours later to house-arrest. Judge Rivka Friedman-Feldman ruled that while evidence had been presented of crimes, the police had failed to prove a clear connection to Mr Gopstein and the others.

It was not the first time that Mr Gopstein, a veteran activist in the outlawed far-right Kach movement and follower of its founder Rabbi Meir Kahana, had been arrested on suspicion of inciting violence, but charges have never been pressed against him.

He and his supporters argue that they are not racist, but simply following Jewish tradition by advocating against “assimilation”.

The group’s name is an acronym for “To Prevent Assimilation in the Holy Land”. It has also protested against Gay Pride parades.

This week’s arrests were not the first time Lehava was targeted by authorities.

Former Defence Minister Moshe Yaalon tried to get Lehava outlawed as a terror organisation in 2015, but the government failed to establish legal grounds for doing so.

And earlier this year, the Reform Movement’s Israel Religious Action Centre petitioned the High Court to put Mr Gopstein on trial for incitement to racism and violence, and to treat Lehava as an organised crime group.

The petition said that “Gopstein has been inciting to racism and violence for years and his severe acts have not been met by a response from law enforcement.” 

The police justified this week’s arrests saying that “recently there have been attacks and harassment of minorities in Jerusalem by members of Lehava” and that the group had been expanding its activities.

But in an interview with the Israeli settlement movement website Arutz Sheva, Ben Zion’s wife Anat said her husband “is being persecuted by the police in a sick obsessive manner” and that Lehava was “saving” Jewish women who are in abusive relationships with Arabs.

“On most days we get half a dozen calls for help but on the day of the arrest, we got calls on sixteen cases of girls who regretfully are dating Arabs and the families are crying for help,” Ms Gopstein said.

She accused the Israel of supporting the Jewish Agency, which “works against assimilation of Jews abroad, while here in Israel it’s considered racism and those working against it are arrested.”