PORTADOWN, Northern Ireland (Reuters) -Rioters attacked police with petrol bombs, rocks and fireworks in the Northern Irish town of Portadown on Thursday, a Reuters witness said, as a fourth night of anti-immigrant violence moved to a different part of the British-run province.

Hundreds of masked rioters attacked police and set homes and cars on fire in the Northern Irish town of Ballymena on Tuesday in the second successive night of disorder that followed a protest over an alleged sexual assault in the town.