One of the ten people arrested in the US accused of being part of an alleged Russian spy ring is also accused of using a false Irish passport.

A man named Richard Murphy, born in Philadelphia and living in New Jersey, was instructed to use the false Irish passport, according to details contained in the criminal complaint documents released by the US Justice Department.

The ten have been charged with carrying out deep-cover work in the US to recruit political sources and gather information for the Russian government.

The documents say Mr Murphy flew from Newark airport to Rome in February, where he was instructed to collect an Irish passport in the name of Eunan Gerard Doherty before flying on to Moscow.

The passport was described in a communication as an old 'transit passport'.

The Department of Foreign Affairs said it has learned that one of the people arrested is alleged to have travelled on a forged Irish passport.

A spokesman for the department said it was seeking more information on the allegations.

A statement says the firm position of the Government in relation to the fraudulent use of Irish passports is a matter of public record.

Earlier, Russian Foreign Minister Sergei Lavrov said he is awaiting an explanation on the ten arrests.

In a statement, the US Justice Department said the suspects had been arrested following an investigation lasting several years.

They had been trained by Russia's intelligence service and sent to the US to infiltrate policy-making circles and collect information, the department said.

Some of the alleged spies had been in the US since the 1990s using false identification.

The arrests were made on Sunday in New York, New Jersey, Massachusetts and in northern Virginia, just outside the US capital Washington.

It came three days after President Barack Obama described his visiting Russian counterpart Dmitry Medvedev as a 'solid and reliable partner' at a White House summit.

Foreign relations official Mikhail Margelov said: 'Very contradictory information is coming out, and no conclusions can be drawn from it.'

Russia's foreign intelligence service and the chief spokesman for Prime Minister Vladimir Putin said they had no comment on US allegations.