THE REPUBLIC'S population increased by about 1.6 per cent annually between 2004 and 2006 due to migration alone, said Government Chief Whip Tom Kitt.
"Such a rate of growth is unprecedented in our history, and is also large by international standards.
"For example, the corresponding rate in the UK, where there was also significant immigration due to the EU accession, is estimated to have been about a quarter of the Irish level."
Mr Kitt said the CSO estimated that the labour force grew by approximately 5 per cent per annum in the two years before the 2006 census.
"This is a high growth rate by any standards and, given the strong link between migration and the labour force, a higher rate of immigration would have resulted in an implausibly high growth in employment."
Labour chief whip Emmet Stagg said Minister of State for Integration Conor Lenihan had rubbished the census figures on immigrants and non-nationals working and living in Ireland.
Mr Kitt said he stood over the CSO's figures. From the feedback received from field staff it was considered highly unlikely that non-Irish nationals would have accounted for more than 10,000 of a conjectured under-enumeration.
Caoimhghín Ó Caoláin (SF, Cavan-Monaghan) said there had been concerns that the last census did not give an accurate record of the number of immigrants.
Mr Kitt said he was happy with the coherence between the CSO data sources dealing with non-Irish nationals and with the accuracy of the recent census results relating to those numbers.
