Rioters in Northern Ireland attacked police with bricks, bottles and other missiles on Monday, wounding at least three officers, on a day of parades by the pro-British Orange Order.
Police responded to the rioting by hundreds of nationalist youths in the mainly Roman Catholic Ardoyne area of North Belfast with water cannon and plastic bullets, a Reuters reporter says. At least one gunshot was fired at police.
At least one teenager was taken to hospital from the scene, which was on the planned route of the Orange parade later in the evening.
The marches, whose participants wear orange sashes and bowler hats to commemorate a 17th century victory of Protestants over Catholics, causes tension each year with the Catholic minority, many of whom would like to see a united Ireland.
Northern Ireland has enjoyed relative peace since a 1998 deal ended the predominantly Catholic Irish Republican Army's military campaign to end British rule of the province.
Police reported clashes in several other areas.
Earlier on Monday, there was a small explosion in Armagh county, where one of the biggest parades of the day was taking place. No one was hurt there.