A false Irish passport was allegedly to be used by members of a Russian spy ring arrested in the United States, it has been disclosed.
The Irish Government said officials had been warned about a link to the so-called "deep cover" operation, broken up after years of secret service investigations.
The US Justice Department claimed 10 suspected Russian agents had been on long-term undercover assignments for authorities in Moscow in a bid to infiltrate American policy-making circles.
Court papers claimed one of the defendants, Richard Murphy, was told by his handlers to travel from the US to Rome where he would be given the forged Irish documents.
Officials in Dublin were investigating whether a fake passport was handed over to a spy and whether it was used to get an agent back into Russia.
"The Department of Foreign Affairs has this morning learned that a person arrested in the US on suspicion of espionage activities is alleged to have travelled on a forged Irish passport," an Irish Government spokesman said.
"The Department of Foreign Affairs will be seeking to obtain further information in relation to these reports."
Ten suspected spies - alleged members of Russia's intelligence service, the SVR - were detained by the FBI in a series of raids on Sunday in New York, New Jersey, Massachusetts and near Washington DC.
Court papers filed by US attorneys at the Department of Justice described the suspects as "illegals" and claimed they were given false travel documents to get back to Russia.
It stated: "In early 2010, Moscow Centre provided instructions to Richard Murphy, the defendant, for his trip from the United States to Russia via Italy, where he was to receive a false Irish passport for travel from Europe to Russia."