Sinn Féin president Gerry Adams has described how the IRA acted as a police force in many nationalists areas in Northern Ireland during the Troubles.
He described the "vast majority" of IRA members involved in this as having "high standards and decency", but in reference to issues such as sexual abuse and rape they were "singularly ill-equipped to deal with these matters."
The comments follow allegations made by Belfast woman Maíria Cahill.
Speaking as part of a BBC Spotlight documentary, Ms Cahill said she was raped in 1997 while a teenager and was later interrogated by the IRA about her rape claim.
Ms Cahill went to the police. A case was brought against the alleged rapist and those said to have been involved in the IRA inquiry.
All charges were dropped after Ms Cahill withdrew her evidence.
In a blog, the Sinn Féin president said that the IRA had "shot" alleged sex offenders or expelled them.
Mr Adams said: "The recent allegations made by Maíria Cahill are of serious concern to myself and Sinn Féin."
He said: "While I refute completely Maíria's allegations against myself and Sinn Féin it does raise the significant issue of how allegations of abuse had been handled in the past by republicans".
The Sinn Féin president said that the RUC was a "quasi military" arm of the state which acted against nationalists.
He said that these areas put pressure on the IRA to "fill this policing vacuum".
Mr Adams said: "A professional, accountable and impartial policing service was absent and unattainable in a society that was manifestly unjust".
He claimed that the "IRA itself often viewed this role as a major distraction from its central function"
He said: "Many senior republicans, including me, had major issues with the IRA acting as a policing agency".
What he calls "IRA policing" was "most evident in those areas where it had strongest support."
He said: "The bulk of this activity involved mediation between those in dispute, and went unreported."
Mr Adams outlined action taken in certain cases by the IRA saying they "often punished petty criminals, car thieves, burglars and drug dealers. The IRA, inevitably also made mistakes".
"This included very sensitive areas such as responding to demands to take action against rapists and child abusers. The IRA on occasion shot alleged sex offenders or expelled them" said Mr Adams.
He also dismissed allegations made in the past suggesting the IRA oppressed nationalist areas saying "this was never the case. The IRA could never have sustained itself without popular support".
He said Sinn Féin later encouraged a policy of directing people in sex abuse cases to contact social services, who would in turn contact the RUC.
Speaking directly in relation to Ms Cahill's case, the Louth TD said: "Maíria alleges she was raped, and that the IRA conducted an investigation into this."
He said: "The IRA has long since left the scene so there is no corporate way of verifying this but it must be pointed out that this allegation was subject to a police investigation."
Mr Adams said: "Charges were brought against some republicans who strenuously denied Maíria's allegations. They insist they tried to help her. They were all acquitted by the court."
He added: "Maíria has also accused Sinn Féin and me of engaging in a cover up. That is untrue. When I learned of the allegation that Maíria was the victim of rape I asked her grand-uncle Joe Cahill, a senior and widely respected republican, to advise her to go to the RUC. He did this but Maíria did not want to do so at that time".
He again called on anyone with information about abuse to contact the authorities, adding that "that includes Maíria Cahill".