|Hundreds of youths, many with their faces covered, threw stones and petrol bombs during riots in Belfast
Two men were shot and up to 500 people were involved in sectarian riots in Belfast, in what local politicians describe as the worst violence of its kind in the area for a decade.
Hundreds of youths, many with their faces covered, threw stones and petrol bombs in the Short Strand area, a Catholic enclave in predominantly Protestant east Belfast on Monday night.
The violence comes at the start of Northern Ireland's marching season, a time of annual parades by Protestants, which usually triggers protests by Catholics.
"I cannot remember in the last decade a situation like this in the Short Strand," Colm McKevitt, a member of the regional parliament for the Irish nationalist SDLP party told Irish state broadcaster RTE.
A police spokesman said shots were fired by both sides, but declined to comment on who or what sparked the violence.
Northern Ireland was torn over three decades of violence between loyalists, mostly Protestants, who want it to remain part of the United Kingdom, and republicans, mostly Catholics, who want to unite with Ireland.
A 1998 peace agreement paved the way for a power-sharing government of loyalists and republicans. Violence has subsided over the years, but there are still dissident armed groups.
IRA blamed for 1976 attack
The riots, coincide with the release of an enquiry report that said the Irish Republican Army (IRA) was behind the killing of 10 Protestant textile workers in January, 1976 in one of the deadliest attacks during the three decades of sectarian trouble.
The IRA has always denied involvement in the attack near the village of Kingsmills, county Armagh, when gunmen forced workers off a minibus and shot them dead at close range.
"The only people to blame for this are the sectarian gunmen belonging to the Provisional IRA who murdered them simply because they were Protestant," said Dave Cox, the head of the Historical Enquiries Team (HET), which conducted the enquiry.
The report focuses on claims that guns used in the shootings might be linked to as many as 110 violent incidents, including 37 murders. The individuals involved in the Kingsmill attack were later implicated in the 1998 Omagh bombing carried out by breakaway Real IRA groups.
The Historical Enquiries Team was set up as part of the peace process to re-examine deaths between 1968 and 1998. It is part of the cross-community Police Service of Northern Ireland, which has widespread support among Catholics and Protestants.