Five police officers were injured on Friday night in the worst rioting for weeks in Belfast in a dispute over the flying of Irish flags near a predominantly pro-British area, officials said.

A crowd of more than 100 youths threw bricks and bottles at police officers in Newtownabbey on the northern outskirts of Belfast and at least one car was set on fire, a police spokesman said.

Security sources said the trouble started when pro-British youths tried to remove Irish tricolor flags on lampposts and were challenged by police.

A 1998 peace deal largely ended more than three decades of tit-for-tat killings in the British-controlled province between mainly Catholic Irish nationalists seeking union with Ireland and predominantly Protestant loyalists who want to remain part of the United Kingdom.

But Belfast remains a city divided along religious lines and British flags are flown from lampposts in some Protestant areas, while some Catholic streets are lined with Irish tricolors.

Loyalists held near-nightly riots in December and January after a vote by Irish nationalist councilors to end a century-old tradition of flying the British union flag every day over Belfast City Hall.

There have been a series of bomb alerts in Newtownabbey in recent days. A hoax bomb was found outside a Catholic Church on Thursday night and earlier in the week what police described as two "crude but viable devices" were found at a local business.