The claim was received by Belfast-based newspaper The Irish News using a recognised codeword.
According to reports in Northern Ireland, the claim came from a group referred to as the "New IRA".
The group also admitted carrying out the murder of journalist Lyra McKee in April.
Following the 1998 Good Friday Agreement, the Irish Republican Army (IRA) disbanded.
A 2008 report by the Independent Monitoring Commission (IMC), a watchdog, said the IRA's campaign of violence was "well and truly over," the organisation having abandoned its structures.
But sporadic violence has been continued by dissident groups who rejected the IRA's ceasefire.
The New IRA emerged in 2012 following the merger of a number of small militant groups and the Real IRA.
It is thought to be responsible for a number of attacks since its formation, including the murders of prison officers David Black and Adrian Ismay.
In January, the Police Service of Northern Ireland (PSNI) blamed the New IRA for a bomb detonated in a van outside the courthouse in Derry.
No one was injured, although CCTV showed a group of young people walking past the vehicle shortly before the blast.
Speaking at the time, Assistant Chief Constable Mark Hamilton said: "The new IRA, like most dissident republican groups in Northern Ireland, are small, largely unrepresentative and determined to drive people back to somewhere they do not want to be."