One of the three attackers shot dead in London on Saturday night was carrying an Irish identity card and had lived in Dublin, according to a report Monday by RTE, Ireland's national broadcaster.
Citing police sources, RTE said the man is believed to have been from Morocco and married to a Scottish woman.
"An Garda Siochana providing every assistance to our colleagues in the London Metropolitan Police in relation to the terror attack in London," the Irish police force said in a statement to AFP.
"We will process all requests from the UK authorities in relation to enquiries into individuals, identities or any other matter," it said.
RTE said officers at the Garda National Immigration Bureau (GNIB) were checking records to establish the residency of the man, who has yet to be identified by name, and his marital status while he was living in the country.
The nature of the card has not been divulged but sources said it was most likely to have been either a GNIB identity card or an Irish EU Fam Card, a type of residency card for non-EU citizens linked to an EU resident in Ireland.
Non-EU citizens who move to Ireland must register with immigration authorities on arrival, and if they stay for more than three months they must apply for a GNIB identity card and carry it with them at all times.
Alternatively, the man may have been granted an EU Fam Card on the basis of his relationship with an EU citizen in Ireland.
An Garda Siochana is also responsible for national security in Ireland, which does not have a separate intelligence service.