The New IRA militant Irish nationalist group has apologised for the killing of journalist Lyra McKee — its first acknowledgement that one of its members was involved, the Irish News newspaper reported on Tuesday.

The organisation, which opposes Northern Ireland's 1998 peace deal, described McKee's death as tragic and offered “full and sincere apologies” to her partner, family and friends in a statement the Irish News said it received on Monday night that used a recognised code.

The 29-year-old reporter was shot dead in Londonderry on Thursday as she watched Irish nationalist youths attack police following a raid. Police said McKee was hit when a gunman opened fire in the direction of officers.

McKee's death, which followed a large car bomb in Londonderry in January that police also blamed on the New IRA, sparked outrage in the British-run province and raised fears that small marginalised militant groups are trying to exploit political tensions caused by Britain's decision to leave the European Union.

The New IRA said it had sent members to the area after the police raid in Londonderry last week. “We have instructed our volunteers to take the utmost care in future when engaging with the enemy, and put in place measures to help ensure this,” its statement said.

The group is one of a number of small organisations that remain active and oppose the 1998 deal, which largely ended three decades of violence in the region. It is far smaller than the Irish Republican Army (IRA), which disarmed after the peace deal.

Police said they unconditionally released a 57-year-old woman arrested earlier on Tuesday in connection with the killing. Two men, aged 18 and 19, were arrested and later released over the killing at the weekend.

McKee's death occurred amid a more than two-year political vacuum in the Northern Ireland since Irish nationalists Sinn Fein withdrew from the compulsory power-sharing government with the pro-British Democratic Unionist Party (DUP).

The executive is central to the 1998 deal and Britain's Northern Ireland minister, Karen Bradley, said on Tuesday she plans to hold talks with party leaders in the province later this week to see what progress can be made.

Irish Foreign Minister Simon Coveney, who has brokered the on-off negotiations between the parties alongside Bradley, also met with politicians in Belfast earlier on Tuesday, his spokesman said.

The last set of talks ended in failure over a year ago and attempts to break the deadlock have been complicated by poor relations between Sinn Fein and the DUP, the DUP's role in propping up Conservative Prime Minister Theresa May's minority government in London and the impact of Brexit on Northern Ireland.

“Our lasting tribute to Lyra must be that to ensure that we continue to work for peace in the whole of Northern Ireland,” Bradley told the British parliament.