The police officer who was killed in Londonderry has been named as Constable Philippa Reynolds.
Two men have been arrested over the crash in the early hours of Saturday morning, which is believed to have involved a stolen car.
The 27-year-old officer on routine patrol when the fatal incident happened at around 3.40am.
Two other officers in the police car sustained non-serious injuries.
The arrested men are aged 23 and 25. They are currently being questioned in police custody.
Chief Constable Matt Baggott has vowed to bring to justice those responsible for the car crash.
Fianna Fáil Leader Micheál Martin has offered his condolences.
Deputy Martin commented: “I want to offer my sincere sympathies on behalf of the Fianna Fáil organisation to the family of the 27 year old officer who lost her life in Derry last night, to Chief Constable Matt Baggot, Minister David Forde and all her colleagues at this very sad time.
“This deeply tragic incident, in which two other officers were also injured, serves as another reminder of the sacrifice men and women on this island make every day in serving on the frontline in our emergency services.
“There is a strong and deepening relationship between the Gardaí and the PSNI and I know the thoughts and prayers of gardaí across the country will be with the officer’s family and her colleagues at this time.”