Police in Northern Ireland say the dissident republican group the New IRA was probably responsible for the fatal shooting of a journalist during overnight rioting in the city of Londonderry.
The Police Service of Northern Ireland said 29-year-old journalist and author Lyra McKee died after she was shot during rioting in the Creggan area.
Assistant Chief Constable Mark Hamilton said a gunman fired a number of shots at police during the unrest Thursday evening.
"We believe this to be a terrorist act. We believe it has been carried out by violent dissident republicans," he said.
"Our assessment at this time is that the New IRA are most likely to be the ones behind this and that forms our primary line of inquiry."
A murder investigation been launched but there have been no arrests. Hamilton appealed for calm to prevail on Easter weekend.
An eyewitness told the BBC that a gunman fired indiscriminately into a crowd during riots on the crowded Creggan housing complex.
The New IRA is a small group of republicans who reject the 1998 Good Friday agreement that marked the Irish Republican Army's embrace of a political solution to the long-running violence known as The Troubles that claimed more than 3700 lives.
The group is also blamed for a Londonderry car bombing that did not cause any injuries in January.
There has been an increase in tensions in Northern Ireland in recent months with sporadic violence, much of it focused in Londonderry, also known as Derry.
Australian Associated Press