Eight police officers were injured when violence broke out at a republican bonfire in Belfast.
Police arrested eight people in what they described as "serious public disorder" in the Divis area near the city centre overnight.
A Police Service of Northern Ireland (PSNI) spokesman said: "Police were attacked by crowds throwing paint bombs, bottles and masonry.
"Eight officers were injured, two requiring hospital treatment for head injuries.
"Eight arrests were made for public order offences and a number of streets in the area were closed for several hours."
Trouble spread northwards to the city's republican New Lodge area where officers were attacked by a man wielding a sword. Officers said they discharged two baton rounds in response to that incident.
The Divis bonfire was built to mark the anniversary of the introduction of internment without trial in Northern Ireland during the Troubles.
Republican groups are due to hold an anti-internment parade through Belfast city centre later. A number of loyalists are set to stage protests along the route.