The row over the flying of the Union flag at Belfast City Hall has led to a sixth successive night of clashes in Northern Ireland's capital.
Hours after the latest violence, the flag was raised there to mark the birthday of a member of the British royal family, Catherine, Duchess of Cambridge, the wife of Prince William, the UK's future king.
The decision by Belfast city council to restrict the flying of the Union Flag to 18 days each year, including royal birthdays, has angered some Unionists.
Around 100, mostly teenagers, attacked police on Tuesday night, fewer than in previous rioting. The police did not have to use water cannon and plastic baton rounds to stop the violence as they did on Monday.
The flag issue has inflamed sectarian passions in Northern Ireland, where Protestants mainly want to stay in the United Kingdom and Catholics want to unite with the Republic of Ireland.