Sinn Féin has claimed that it uses its influence in the United States "very positively".
The party has been criticised after it placed ads in US papers calling for Irish unity ahead of St Patrick's Day.
Taoiseach Leo Varadkar said placing advertisements in the likes of The New York Times and Washington Post is not helpful.
Mr Varadkar is in Washington DC to meet the US president with the 25th anniversary of the Good Friday Agreement high on the agenda.
He said: "I just don't think that's helpful [unity adverts] at this time, I'm somebody who believes in unification but I don't think that's helpful at this time.
"It's a sensitive moment, we're trying to get everybody on board for the Windsor Framework, and we shouldn't forget what the Good Friday Agreement says... we're marking 25 years of the Good Friday Agreement this year.
"It brought peace to Ireland, what does it say? It says that there can be a Border Poll when it's clear that a majority of people North and South would vote for it, that's not clear at all at the moment."
However, Sinn Féin TD David Cullinane said any work the party does in the US is in Ireland's best interest.
'Political opponents'
Mr Cullinane told Newstalk: "I think that Sinn Féin has used its influence in the US very positively, so any criticism that is levelled at Sinn Féin is obviously political... coming from political opponents.
"Most reasonable people see that the work Sinn Féin does in the US is about advancing the peace process and about advancing Irish interests."
A former taoiseach has also criticised Sinn Féin for placing ads in American newspapers, arguing that it does little to further the cause of Irish unity.
John Bruton has described the move as "counterintuitive".
Mr Bruton said: "In accordance with a principle of consent, a majority in Northern Ireland, and if we want unity in peace, a substantial majority of unionists in Northern Ireland, have to come around to the view that unity is in their best interests. Placing adverts in the American papers doesn't contribute to that."
