BELFAST, NORTHERN IRELAND (CNN) - Sectarian violence flared up Saturday in Northern Ireland as Protestants continued their annual marching season in a predominantly Catholic city.
Violence erupted earlier in Londonderry, also known as Derry to some residents, when masked youths attacked police vehicles with petrol bombs and a pipe bomb, setting fire to and hijacking a number of vehicles.
The clashes followed the annual Apprentice Boys' parade, when about 10,000 Protestants marched in remembrance of the 1689 anniversary of the siege of Derry by England's Catholic ruler James II.
Police said protesters hurled several dozen petrol bombs and a mail van was later hijacked and set on fire as the main parade started.
The Police Service of Northern Ireland warned members of the public to avoid the area.
Three people have been charged in connection with the disorder, with several more arrested, police said.
The area was later reported quiet, with local sources describing the earlier violence as "sustained rioting during a short period of time."
However, there was further sporadic violence later in the evening.
Derry's hard-line Catholic, republican-nationalist groups opposed to the Irish peace process have reacted violently in previous years to these annual Protestant marches, seeing them as provocations.
Protestant groups claim they have the right to follow their centuries-old tradition.
There was rioting earlier in the summer with some of the worst violence in the Ardoyne area of north Belfast following a parade by the main Protestant marching organization, the Orange Order.
The province suffered decades of violence known locally as the Troubles, in which more than 3,500 people were killed before a 1998 peace accord known as the Good Friday Agreement.
The Troubles pitted mostly Catholic republicans, who want the province to become part of the Republic of Ireland, against pro-British loyalists, who are mostly Protestant.
This year has been one of the most violent since the Good Friday Agreement.
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