Catholic youths attacked police with petrol bombs in the Northern Ireland city of Londonderry on Saturday ahead of one of the largest Protestant parades of the year.
Thousands of pro-British unionists were due to take to the streets of the city for the annual Apprentice Boys parade, which marks the ending of the siege of Derry by Catholic King James II in 1689.
Pro-British Protestants march every summer to commemorate historical events, sometimes triggering a violent response from mainly Catholic Irish Republicans.
Police said at least 25 petrol bombs and fireworks were thrown at officers as they investigated a suspected bomb that turned out to be a hoax, but no injuries were reported. Police said they had been called to investigate several suspicious objects across the province.
A peace deal signed in 1998 largely ended three decades of violence between Catholics and Protestants that led to the deaths of more than 3,600 people, but much of the British province remains divided along religious lines.
(Reporting by Ian Graham; Editing by Conor Humphries and Stephen Powell)