The Irish convert, who spoke at a press conference organised by a prominent Dublin Imam last Friday, also claimed there were 150 extremists living here.
While counter-terrorism officers stress they do not yet know if, or to what extent, the claims are accurate, sources said they were taking them “very seriously”.
Gardaí have already identified that one of the terrorists, Rachid Redouane, had lived in Ireland, with known addresses in Dublin.
An Irish woman from Limerick, referred to as Aaliyah, told the media that a second London attacker and suspected ringleader, Khuram Butt, had also been in Ireland.
Butt was known to police and MI5 after publicly associating himself with hate preacher Anjem Choudary and other extremists in his Islamist network, al-Muhajiroun.
Aaliyah, who converted when she was 18, associated with Choudary’s network in Britain and was engaged to one of its associates.
The now 26-year-old told the media that not only had Redouane been in Ireland but so too had Butt.
She claimed she saw Butt in Ireland “two or three times” and that he and other extremists operated out of a house in the Santry area of north Dublin and that many of them also lived in properties in Limerick, Clare, and Tipperary.
She claimed Butt was “visiting people” in Ireland and “giving talks” while staying here for a few weeks “on and off”. She claimed the dream of the extremists here was “to have an army for jihad”.
The woman said she was deradicalised with the assistance of a London-based Imam and his wife. Recently she approached Dr Umar Al-Qadri, imam of the Islamic Cultural Centre in Blanchardstown, west Dublin.
Garda security officers have interviewed Aaliyah at length and are now investigating her claims. “Absolutely, this is a serious development, if what she says is true,” said one source.
“Inquiries are being conducted to see can we confirm or dismiss the claims.”
It is not known how specific Aaliyah has been in terms of addresses, when she was here, names or contact details of landlords, and names of other extremists that were present.
“If what she says is true it would change our attitude to things, but it is early days in the investigation,” said a source.
Detectives will try and piece together any contact between Redouane and Butt here and will examine the extremely serious issue of whether any “pre-planning” for the London attacks occurred here.
Gardaí are likely to contact the London Met and ask them to interview the London imam about Aaliyah’s story. Members of Counter Terrorism International will try and locate and interview any relevant persons here.