Jerusalem - Tens of thousands of black-clad ultra-Orthodox Jews staged mass demonstrations on Thursday to protest a Supreme Court ruling forcing the integration of a religious girls' school.

Protesters snarled traffic in Jerusalem and another large religious enclave, crowded onto balconies in city squares, and waved posters decrying the court's decision and proclaiming the supremacy of religious law.

It was one of the largest protests in Jerusalem's history, and a stark reminder of the ultra-Orthodox minority's refusal to accept the authority of the state.

Also, the throngs of devout Jews showed to which extent the ultra-Orthodox live by their own rules, some of them archaic, while wielding disproportionate power in the modern state of Israel.

Parents of European, or Ashkenazi, descent at a girls' school in the West Bank settlement of Emanuel don't want their daughters to study with schoolgirls of Mideast and North African descent, known as Sephardim.

The Ashkenazi parents insist they aren't racist, but want to keep the classrooms segregated, as they have been for years, arguing that the families of the Sephardi girls aren't religious enough.

Israel's Supreme Court rejected that argument, and ruled that the 43 sets of parents who have defied the integration efforts by keeping their daughters from school were to be jailed on Thursday for two weeks.

Police spokesman Micky Rosenfeld said about 100,000 people converged in downtown Jerusalem in support of the Ashkenazi parents. An additional 20,000 demonstrated in the central city of Bnei Brak.