The so-called New IRA has admitted responsibility for the murder of journalist Lyra McKee in Derry.
Miss McKee, 29, 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 offered "full and sincere apologies" to her family and friends.
The New IRA is an amalgam of dissident paramilitary groups opposed to the peace process and it recently claimed responsibility for parcel bombs sent to London and Glasgow in March.
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."
One of Northern Ireland's most promising journalists had her dreams snuffed out in a barbaric killing, her partner has said.
"Our hopes and dreams and all of her amazing potential was snuffed out by this single barbaric act," Sarah Canning said.
"Victims and LGBTQI community are left without a tireless advocate and activist and it has left me without the love of my life, the woman I was planning to grow old with," she added.
"This cannot stand, Lyra's death must not be in vain because her life was a shining light in everyone else's life and her legacy will live on and the life that she has left behind."
Ms McKee was an editor for California-based news site Mediagazer, a trade publication covering the media industry.
In 2016, Forbes Magazine named her one of their 30 under 30 in media.
She had been working on a new book which had been due to be published in 2020.
Michelle Stanistreet, National Union of Journalists (NUJ) general secretary, said Ms McKee was one of the most promising journalists in Northern Ireland.
She said: "A young, vibrant life has been destroyed in a senseless act of violence.
"A bright light has been quenched and that plunges all of us into darkness."
Causes close to her heart included helping homeless people, preventing suicide and supporting LGBT rights in the most restrictive regime in Europe.