The dissident republican group calling itself the 'New IRA' has admitted responsibility for the murder of journalist Lyra McKee.
In a statement to The Irish News, using a recognised codeword, the group offered "full and sincere apologies" to the 29-year-old's family and friends.
Reacting to the statement, Lyra McKee's friend Sinead Quinn said it "means nothing" and "gives no-one comfort".
Meanwhile, a 57-year-old woman who was arrested under the Terrorism Act in connection with Lyra McKee's murder has been released unconditionally.
"Detectives from PSNI Major Investigation Team continue to appeal for help from the local community in Creggan or anyone with information," police said.
Lyra McKee died after being shot in the head during rioting in the Creggan area of Derry last Thursday night.
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 'New IRA' statement said: "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 andfriends of Lyra McKee for her death."
Sinead Quinn, a friend of Lyra McKee, said the apology "doesn’t change the events of the last few days, which have been intolerable".
She added: "It gives no-one comfort and in fact the way their statement continued on, which is basically ‘we’re no going to go away’, that flies in the face of the apology.
"So an apology without actually positive action means nothing."
As investigations into the shooting continue, the lead detective has said he believes he knows who the gunman was, but is appealing for more information.
Det Supt Jason Murphy said there has been “significant progress” in the investigation and a “huge outpouring of support” from the local community.
He added that he has spoken to the Public Prosecution Service about "protection measures" for witnesses coming forward.
Meanwhile Lyra McKee's funeral will take place on Wednesday.