Ten PSNI officers were injured as police dealt with several hours of trouble in Londonderry.
Fireworks, petrol bombs and other missiles were used to attack police as violence flared in the Nailors Row area last night.
The Public Order Dog Unit was deployed as part of the response.
Up to 50 young people were behind some of the violent scenes.
At one stage police appealed to parents to “come and bring their children home”.
Today, a senior PSNI officer said the scenes were “unacceptable”.
Derry City & Strabane Superintendent William Calderwood said: “The scenes we witnessed were disgusting, and I want to commend our officers for their professionalism.
“These were difficult conditions for officers from across numerous departments.
“To see our officers injured as a result of this violence is appalling. It is completely unacceptable.”
Mr Calderwood said one arrest has been made so far.
“We can reassure you a robust investigation is underway to bring all those responsible for this violence to justice,” he added.
“I want to make it clear this violence involved individuals who were intent on attacking police, and who exploited an increased police presence in the city yesterday to do just that.”
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He added: “We know from the work our officers do on a daily basis that last night’s disgraceful and senseless violence will have provoked anger in the local community and wider area.
“The public can be reassured you will see our officers on duty today, continuing to work with communities, and working to keep people safe.”
Foyle MP Colum Eastwood said the disorder was “disgusting”.
Writing on X, he said that “putting children in this position is nothing short of child abuse. Derry, resolutely, opposes this senseless violence.”
Sandra Duffy, a Sinn Féin councillor and former mayor of Derry City and Strabane, said “a small number of young people” were involved in the trouble.
“Ongoing petrol bomb attacks on police at Bishop Street are a disgrace and must stop now,” she said.
“I am also concerned about vulnerable and elderly residents at Alexander House who do not need this activity on their doorstep.”
Ms Duffy urged other young people not to get caught up in the violence “as it could have a negative impact on their future”.
“These futile actions are wrong and they are not representative of this city,” she said.
“They are in stark contrast to the hugely positive work and positive community events taking place across the Bogside this week.”