A 57-year-old woman who was arrested in connection with the murder of journalist Lyra McKee has been released.
The woman was held under the Terrorism Act, the Police Service of Northern Ireland said.
The 29-year-old, died as a result of injuries sustained when she was shot on the Creggan estate on April 18.
In a statement given to The Irish News using a recognised code word, the group admitted responsibility, offering “full and sincere apologies” to her family and friends.
It said she was killed after volunteers were sent to "engage the enemy" - which it described as "armed British crown forces".
In a short statement, the PSNI did not disclose any further details about the nature of the arrest, only that she had been taken to Musgrave Serious Crime Suite.
Two teenage men initially arrested by detectives investigating the murder were later released without charge.
The arrested 57-year-old woman was released unconditionally on Tuesday night.
Detectives from the PSNI Major Investigation Team continue to appeal for help from the local community in Creggan or anyone with information.
Police believe the violence was orchestrated in response to an earlier search by officers aimed at averting imminent trouble associated with this week’s anniversary of the Easter Rising.
The statement said: “On Thursday night, following an incursion on the Creggan by heavily armed British crown forces which provoked rioting, the IRA deployed our volunteers to engage.
“We have instructed our volunteers to take the utmost care in future when engaging the enemy, and put in place measures to help ensure this.
“In the course of attacking the enemy Lyra McKee was tragically killed while standing beside enemy forces.
“The IRA offer our full and sincere apologies to the partner, family and friends of Lyra McKee for her death.”
On Monday, friends of Miss McKee have defaced an office belonging to the New IRA by putting red handprints on the walls of its headquarters in Londonderry.
A number of Miss McKee’s friends walked to Junior McDaid House in Derry, where they used a pot of red paint to place hand prints on the side of office walls.
A group of some six men, understood to be members of republican group Saoradh, who are associated with the New IRA, stood outside the building during the intense protest.