A woman has been arrested under the Terrorism Act in connection with the murder of journalist Lyra McKee in Northern Ireland as the paramilitary group responsible for the attack issued a statement apologizing for the slaying.

Authorities in Northern Ireland say the 57-year-old woman was detained on Tuesday. Her identity remains unknown.

McKee, the slain journalist, was killed by gunfire last week during a riot in the city of Londonderry in Northern Ireland.

JOURNALIST SHOT DEAD IN NORTHERN IRELAND RIOTING, POLICE CALL IT ‘TERRORIST ACT’ BY NEW IRA GROUP

Police called the incident a “terrorist act” and suggested the group calling itself the New IRA, a splinter group of Irish Republican Army, was behind the attack.

“We believe this to be a terrorist act,” Assistant Chief Constable Mark Hamilton said. “We believe it has been carried out by violent dissident republicans.”

Last week, two teenagers were arrested under the anti-terrorism law, but they were shortly released, as authorities continue to scramble to find the exact perpetrators of the murder.

The New IRA admitted Tuesday in a letter that one of their “volunteers” killed the journalist during the riot in the city, according to the Irish News.

GROUP CALLING THEMSELVES THE IRA CLAIMS RESPONSIBILITY FOR LETTER BOMBS IN UK

“The IRA offer our full and sincere apologies to the partner, family and friends of Lyra McKee for her death,” the letter read, which also accused the police of purposely “provoking” the riots.

“The IRA offer our full and sincere apologies to the partner, family and friends of Lyra McKee for her death.” — The New IRA

“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,” it added.

The letter added that McKee was killed “while standing beside enemy forces,” which refers to police forces. Authorities suspect that it was a stray bullet that hit the woman.

CLICK HERE FOR THE FOX NEWS APP

The New IRA is a small group of republicans who reject the 1998 Good Friday agreement that marked the Irish Republican Army's embrace of a political solution to the long-running violence known as "The Troubles" that claimed more than 3,700 lives.

The Associated Press contributed to this report.