JERUSALEM - Ultra-Orthodox Jews throwing rocks and firecrackers clashed with police using horses and water cannon in Jerusalem on Thursday, in the third day of rioting over the arrest of a mentally ill Hasidic woman who authorities say was starving her child.

Late in the day, the unrest spread to a city outside Jerusalem with a large ultra-Orthodox population, where dozens of protesters tried to block a road.

The clashes in Jerusalem involved hundreds of rioters and spread to several ultra-Orthodox neighbourhoods of the city. They are the latest sign of increasing tensions between authorities, who allege the woman starved her 3-year-old son over several years, and the insular ultra-Orthodox community, which often resents outside interference in its affairs.

Hospital spokeswoman Yael Bossem-Levy confirmed that the woman is suffering from a condition known as Munchausen syndrome by proxy, in which a person deliberately makes another sick. Her child is hospitalized.

Tensions between authorities and ultra-Orthodox Jews, who make up a third of Jerusalem's residents, have been high since voters replaced an ultra-Orthodox mayor with a secular candidate in a November election.

In recent weeks, ultra-Orthodox Jews and authorities have clashed repeatedly over a decision by Jerusalem Mayor Nir Barkat to open a municipal parking lot on the Sabbath. Ultra-Orthodox Jews oppose the idea because driving is forbidden on the Sabbath.

In the wake of this week's disturbances, City Hall has cut off municipal services to some ultra-Orthodox areas, saying it can't guarantee the safety of its workers.

In the first wave of protests Thursday, rioters lobbed rocks and explosives, set dozens of trash bins ablaze and strewed garbage across city streets. Police used horses and a water cannon to contain the unrest.

On Thursday night, several dozen ultra-Orthodox tried to block a major thoroughfare but were dragged away by police, Jerusalem police spokesman Shmuel Ben-Ruby said. Elsewhere in the city, protesters lobbed cherry bombs and rocks at officers, he said in a pager statement.

Fifteen people were arrested, 20 were detained for questioning and 10 police officers were slightly wounded, he said.

In Beit Shemesh, about 20 miles outside Jerusalem, about 100 protesters tried to block a road but police were evacuating them, he added.

On Thursday, protesters demonstrated outside the hospital where the 3-year-old is being treated. The Israeli daily Yediot Ahronot published a photograph of the emaciated child and reported that his weight was 15 pounds (7 kilograms).

His mother, who has not been identified, was in police custody. Authorities say they have video footage showing her disconnecting him repeatedly from a feeding tube at the hospital.

The woman claims the child is sick and that she is not responsible for his condition, a position accepted by many of those protesting her arrest.