There are "five to six" cases of Irish citizens detained by US Immigration and Customs Enforcement (ICE), Taoiseach Micheál Martin has said.
Speaking in the Dáil, Mr Martin said the cases "vary in terms of status" but said the Government would do everything it can to help Seamus Culleton, who has been detained by ICE since September.
Mr Culleton, originally from Glenmore in Co Kilkenny, was picked up by Immigration and Customs Enforcement agents last September and taken to a detention centre in Texas, almost 4,000km away from his home in Boston.
The Taoiseach said efforts to assist Mr Culleton had to be done in a way that could really help him and be effective.
He said it was important not to do anything to make Mr Culleton's situation more difficult.
He was responding to Labour leader Ivana Bacik who called on the Government to pull out every stop and every diplomatic lever to have him released.
She said it could not wait until St Patrick's Day when the Taoiseach is due to meet US President Donald Trump.
She said it was ironic that one arm of the US government was processing Mr Culleton for permanent residency while the other had him locked in a cage.
Ms Bacik also said that deportations of Irish citizens from the US had quadrupled in the past year.
She said there was no sense of urgency from the Government.
Minister for Foreign Affairs Helen McEntee said she is aware of a small number of people in situations similar to Irish man Seamus Culleton, who was detained by immigration officials in the US last year.
While Mr Culleton has been undocumented in the US for a time, he was in the final stages of receiving his Green Card and had a valid work permit.
However, he told RTÉ's Liveline programme that none of that mattered after he was followed and then arrested by ICE agents.
He was speaking to the programme from the detention centre in El Paso, where he said that he feared for his life.
"You don't know what's going to happen on a day-to-day basis," Mr Culleton said.
"You don't know if there's going to be riots, you don't know what's going to happen. It's a nightmare down here."
Watch: Small number of Irish people in situations similar to Culleton, says McEntee
Speaking as she arrived for this morning's Cabinet meeting, Ms McEntee said that assistance was being provided to Mr Culleton and his family.
"We've made it very clear that the embassies right across the US are there to support any citizen in any situation they're in, but only a small number of people have come forward," she said.
The minister did not give an exact number of cases but agreed that the figure was less than a dozen.
DFA officials dealing with US Homeland Security and ICE
Earlier, the Taoiseach said that officials in the Department of Foreign Affairs and the Irish embassies are dealing with the US Homeland Security and ICE agencies in relation to Mr Culleton's case.
Mr Martin was asked whether he would be raising Mr Culleton's case with US President Donald Trump when he visits the White House next month.
Mr Martin said that he would like to see Mr Culleton leaving the ICE facility he is being detained in.
He said that the Government has been concerned about undocumented Irish people in the US for a long time, "long before President Trump came into office".
"There is now a crackdown in America in terms of the implementation of migration law which we are concerned about in terms of how it affects the Irish undocumented," he said.
Social Democrats Senator Patricia Stephenson said the Culleton family has felt isolated by the Government and were forced to go public with his case as a result.
Speaking outside Leinster House, she said: "It really shouldn't take families coming out publicly for the Government to take action.
"We heard from the Taoiseach that they have been in touch, but the family are not reporting substantial support."
Ms Stephenson said she and the Culleton family have been put in contact with Massachusetts Senator Ed Markey in order to get "direct in-country representation" for Mr Culleton.
"I felt the need to do that simply because I don't have a huge amount of faith in the Irish Government to take action on this, more than they've already been doing," she added.
Additional reporting Harry Manning, PA
