29-year-old McKee was shot dead in the Creggan area of Londonderry, calling the Northern Ireland police a "terrorist attack". The prominent freelance journalist had written for publications such as The Atlantic and Buzzfeed News.
Called Londonderry by Irish nationalists Derry and British Unionists, the city is only a short drive from the border with the Republic of Ireland.
"Investigators from the main investigative team arrested a 57-year-old woman under the Terrorism Act in connection with the murder of Lyra McKee," the police said in a tweet.
In a statement to the Irish News, in which the newspaper referred to as a "recognized codeword," the group said, "During the attack on the enemy, Lyra McKee was tragically killed when she stood next to the enemy forces."
"The IRA offers our partner, family and friends of Lyra McKee our full and sincere apology for their death," said the statement. "We have instructed our volunteers to use the utmost care in the intervention of the enemy in the future and to take measures to ensure this."
According to The Irish News, the alleged statement of the New IRA was signed with the name "T O & # 39; Neill".
CNN did not independently verify the authenticity of the statement and contacted the Northern Ireland police to comment.
According to Detective Superintendent Jason Murphy, McKee was killed by shots fired "indiscriminately."
"The shots were fired in a residential area at a time when many locals were on the street, including children," Murphy told the media. "The gunman had no idea who might have been killed or injured in these shots."
Pictures showed vehicles burning when a crowd threw fireworks and gasoline bombs a day before Good Friday on the night of the riots.
During the Easter weekend, Republicans trying to unite Northern Ireland-ruled Northern Ireland with the Republic of Ireland celebrate the anniversary of the 1916 Dublin uprising against British troops. The Easter Rising, which was taken at a time when all Ireland was under British rule, is considered one of the most important dates in the struggle for Irish independence.
The police were in the Creggan area looking for "violent Republicans" whom they believed held firearms and explosives for planned attacks, possibly over the Easter weekend.
Who is the new IRA?
The original IRA was active in the struggle for Irish independence from British rule in the 20th century before the creation of the Irish Free State. The group, commonly known as IRA, is actually called Provisional IRA. on A paramilitary Irish nationalist group active during the "Troubles" – the decades-long sectarian conflict in Northern Ireland that killed more than 3,500 people and was ended by the 1998 Good Friday Agreement.
It is feared that Brexit could encourage the revival of sectarian violence.