Jerusalem's city centre is witnessing a backlash against hard-line right-wingers who take to the streets on popular clubbing nights to form a self-declared "honour guard" against Jewish-Arab relationships.

The controversial Lahava organisation arranged high-profile demonstrations outside the recent wedding of Morel Malka, a Jewish convert to Islam, and her Arab partner Mahmoud Mansour. It also runs a hotline for people to report mixed faith romances so that its activists can persuade the Jewish partner to break it off.

Lahava's chairman, Benzi Gopstein, said that by setting up a stall in Jerusalem on busy nights, his group is breaking the silence on assimilation.

"We all hear about assimilation all over the world, but in Israel no-one speaks about it," he said, adding: "The message is that Jews need to date and marry just Jews."

But critics say that the activists cross the line from discussion to harassing couples on the streets whom they believe to be mixed faith, and claim that they sometimes turn violent. The accusations are denied by Mr Gopstein. They point out that Mr Gopstein is not from Israel's political mainstream but rather - by his own admission - a follower of the late rabbi Meir Kahane, whose party was banned from Knesset for racism.

Ofek Birnholtz, a doctoral student at Hebrew University, runs a secular-religious group which opposes Lahava on the streets. Mr Birnholtz said: "We try to counter their presence, saying they cannot dominate the public sphere."

He acknowledged that Judaism has a problem with mixed marriages but said that Lahava had stepped beyond the boundaries of reasonable discussion to become a "racists' supremacy group".