A 57-year-old woman has been arrested in connection with the murder of journalist Lyra McKee in Londonderry.
The woman was arrested under the Terrorism Act, the Police Service of Northern Ireland said.
Ms McKee, 29, died as a result of injuries sustained when she was shot on the Creggan estate on April 18.
The arrest comes after the New IRA admitted responsibility for the journalist’s killing.
In a statement given to The Irish News using a recognised code word, the group offered "full and sincere apologies" to her family and friends.
The New IRA is an amalgam of armed groups opposed to the peace process and it recently claimed responsibility for parcel bombs sent to London and Glasgow in March.
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."
The senior detective leading the investigation into Ms McKee’s murder has revealed that since her death more than 140 people have contacted police with information.
Detective Superintendent Jason Murphy said the investigation to find her killer is continuing at a "rapid pace".
Mr Murphy said: "We've had a massive public positive response to the investigation since Thursday evening.
"This was an attack on the community. Lyra, tragically, was a random victim and I need the public to continue to support us.
"Many witnesses have contacted us to give us information that has been provided to them. More than 140 people have contacted us via our MIPP with messages, including mobile phone footage.
"House-to house enquiries are continuing, and all of that is to be welcomed."
He added: "My appeal today to witnesses who haven't come forward to us is simple. Please, come forward and have a conversation with me. Come and talk to me.
"I want to reassure people that you don't have to commit to anything today. I just need to speak to people to understand what they know.
"We can then look at how we capture that information in the best way possible to protect those witnesses and enable me to bring the gunman who killed Lyra McKee to justice."
The appeal came after friends of the journalist protested by defacing an office belonging to a dissident republican group 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 handprints on the side of the 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 protest.
PSNI officers were also present and later asked for the names of those involved in the incident.
Lyra's friend Sinead Quinn, who took part on Monday's protest, said: "We have used red paint because they have blood on their hands for what has happened.
"They have encouraged it, they have moulded these young people into what they are and they are standing behind them handing them guns.”