A Russian diplomat has been asked to leave the country after a garda investigation showed that Russia's intelligence services had forged Irish passports for use by a US-based spy ring.

'The activities of Russian intelligence services in connection with the forgery of Irish passports and the effective theft of the identity of six Irish citizens are completely unacceptable,' the Department of Foreign Affairs said in a statement.

The Department's secretary general told the Russian ambassador in Dublin that the accreditation of one of his staff had been terminated and the diplomat has been asked to leave Ireland by a specified date.

'The government, by today's action, has once again made clear that it will not tolerate the fabrication and use of forged Irish passports by agents of a foreign state,' it said.

'It is hoped that it will be possible to move on from this disturbing incident and to develop further the relationship between Ireland and the Russian Federation.'

Irish passports are highly prized by secret agents and terror groups because Ireland's neutral status means that its citizens are welcome in most countries.

In June, the Government called on Israel to withdraw a staff member at its Dublin embassy over the use of fake passports in the killing of a Hamas commander in Dubai.