BELFAST, Aug 11 (SPA) - Rival gangs hurled petrol bombs, bricks and bottles at police during overnight disturbances in Northern Ireland's second city Londonderry, a police spokesman said on Wednesday. The trouble, the latest in a series of incidents in Londonderry in recent days, comes ahead of a traditionally divisive Protestant parade in the city at the weekend. Police said they were attacked after being called to deal with clashes between Catholic and Protestant gangs in the Waterside area of the city. "Rival groups had gathered in the area and threw a number of stones, bottles and bricks at each other," said a police spokesman. "Bricks and bottles were also thrown at police, as well as two petrol bombs." On Saturday, thousands of members of the Protestant Apprentice Boys will parade around the city's historic stone walls to commemorate the relief in 1689 of a Protestant garrison besieged by Catholic forces. In the past the event has often provoked violence, although in recent years it has been largely peaceful following negotiations between parade organizers and Catholic residents' groups. --SPA 1154 Local Time 0854 GMT www.spa.gov.sa/190874