• Disorder spreads including fire at leisure centre
• Smaller crowd clash with police at flashpoint of Ballymena
• Police investigating property attacks as racially-motivated

LARNE, Northern Ireland, June 11 (Reuters) - Masked youths in Northern Ireland on Wednesday set fire to a leisure centre that had been sheltering migrant families, but a third night of anti-immigrant violence was smaller in scale in the primary flashpoint of Ballymena.

Violence first flared on Monday after two 14-year-old boys were arrested and appeared in court, accused of a serious sexual assault on a teenage girl in the town. The charges were read via a Romanian interpreter to the boys, whose lawyer told the court that they denied the charge, the BBC reported.

In the most intense violence on Tuesday, hundreds of masked rioters attacked police and set homes and cars on fire in Ballymena, in what police condemned as "racist thuggery."

On Wednesday, a smaller crowd in the town threw rocks, fireworks and petrol bombs at police, who responded with water cannon.

Nine officers were injured, none seriously, bringing to 41 the number hurt since the violence began, police said in a statement. They added that a hatchet was thrown at police lines during the disorder.

But 30 kilometers east in Larne, masked youths smashed windows and started fires in the lobby of a leisure centre where families whose homes were attacked in Ballymena had been briefly moved, officials said.

Women and children were taking part in swimming and exercise classes when the attack began and had to be evacuated through the fire exit, said a woman who was in the centre at the time.

The crowd was acting "like rabid animals," said the woman, who declined to give her name. She said she felt "frightened and intimidated."

Justice Minister Naomi Long said the attack was "completely unjustified and unjustifiable". Finance Minister John O'Dowd described the attackers as "racist thugs."