Police were injured by flying masonry and a hijacked bus during serious loyalist rioting in Northern Ireland.
A total of six officers were hurt during trouble on Saturday night in Co Antrim, linked to a dispute over flags, which saw angry mobs hurl petrol bombs and other missiles at police lines.
There were appeals for calm as community tensions threatened to boil over ahead of this week's July Twelfth, which marks the culmination of the Orange Order's marching season.
A Catholic church in Co Antrim was damaged with paint over the weekend and on Saturday homes came under sectarian attack in Co Londonderry.
Chief inspector Derek MacCamley said: "It appears at this stage that the disorder was caused predominantly by young people who were intent on attacking the police service. The cost to the police service is high but the cost to the community is much higher.
"The people involved in carrying out these attacks are hurting their own communities. Their actions do not reflect on the vast majority of people who live in the area - who want to live in peace and go about their daily lives without fear or intimidation."
A hijacked bus was used to ram a PSNI vehicle, injuring five officers, and petrol bombs and other missiles were hurled by a crowd of up to 100 loyalists in Ballyclare, Co Antrim. Officers responded with water cannon and baton rounds.
Another police officer was hurt after masonry was hurled. A total of 15 vehicles were hijacked, including two buses. Several were set alight and used to attack police lines. Batons were fired by police in Ballyclare and nearby Carrickfergus and water cannon was used in Ballyclare. There was also less serious trouble in Larne, Co Antrim.
Loyalists in Co Antrim have been protesting after accusing police of removing flags. This is the height of the traditional marching season for the Orange Order and many Protestant districts are flying flags and bunting.
A man, aged 27, was arrested for riotous behaviour in the Co Londonderry town of Magherafelt and homes were attacked by sectarian bigots. Police were targeted with missiles as they tried to remove barricades placed across a road close to a bonfire site.