A 57-year-old woman has been arrested under the Terrorism Act in connection with the killing of journalist Lyra McKee in Londonderry.
Ms McKee, 29, died from her injuries after she was shot on the Creggan Estate while reporting on rioting on Thursday.
Police Service of Northern Ireland said in a short statement on Tuesday: "Major Investigation Team detectives have arrested a 57-year-old woman under the Terrorism Act in connection with the murder of Lyra McKee in Creggan in Derry/Londonderry on Thursday, April 18.
"She has been taken to Musgrave Serious Crime Suite."
The force didn't share any further details about the nature of the arrest.
An Irish Republican Army (IRA) splinter group had earlier said one of its "volunteers" killed Ms McKee.
In a statement issued to the Irish News, the New IRA 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 admission came as police said the investigation into the killing was continuing at a “rapid pace”, with more than 140 people contacting officers with information.
Tuesday's arrest came after police held two men in relation to the killing on Saturday. However, they were both later released.