A police officer has been suspended while the use of CS spray in Londonderry is investigated, the PSNI has said.
CS spray was used to quell disturbances in Derry
The spray was used early on Saturday during disturbances in the city centre.
The PSNI said the spray was a "valuable police instrument" and its use is now automatically referred to the Police Ombudsman.
It said the officer had been suspended as part of an internal police investigation.
The police used CS spray during two separate weekend disturbances in the city centre.
The police said it was used in Victoria car park after a man was attacked by up to 30 youths, and a few hours later in Waterloo Place to break up a fight.
In keeping with police policy, both incidents were referred to the Police Ombudsman.
However, the PSNI is also carrying out its own investigation which has resulted in one officer being suspended while further inquiries are carried out.
The police have not said which incident the officer was involved in.
In a statement on Thursday, the PSNI said it continued "to work proactively to ensure as wide an understanding as possible of CS spray.
"It is an important and valuable police instrument when used as part of a graduated response to individual violence."
CS spray has been used on eight separate occasions in Derry since its introduction in August.
It has been used elsewhere in Northern Ireland 11 times.