Seven people have been arrested in Belfast, the capital of Northern Ireland, after at least 15 police officers were wounded in sectarian rioting.
Amid a rain of petrol bombs and rocks, a van was hijacked and driven into police lines on Monday night, after about 300 Protestant loyalists gathered to protest against a parade held on Sunday by a republican flute band from a nearby Catholic community.
Some 47 people - mostly police - had been hurt in clashes on Sunday.
Police shot plastic bullets and water cannon in an attempt to disperse the crowds who had gathered, as unrest grew over competing marches held by Protestant and Catholic groups.
More than 100 masked, hooded Protestants threw bottles, bricks and fireworks at police lines on Sunday night, the AP news agency reported.
Police commander Matt Baggott said his officers demonstrated "courage and restraint", while Terry Spence, of the Police Federation of Northern Ireland, said that "their bravery and courage is in stark contrast to that of the cowardly thugs responsible for trying to murder them".
Sunday night's violence came as Irish republicans from a Catholic area of the community paraded near Protestant districts of north Belfast, where residents traditionally identify with the British crown.
Protestant groups had previously been prohibited from marching in the area, and many were reportedly frustrated with a lack of restrictions placed on the Catholic band.
The annual marches held every summer have frequently resulted in flaring unrest, though violence has been limited in recent years.
Northern Irish politicians have claimed that the latest violence had been sustained by loyalist paramilitary groups such as the Ulster Volunteer Force and the Ulster Defence Association, though loyalist sources have vehemently denied these claims.