Sinn Féin leader Mary Lou McDonald has been criticised for holding a banner in the New York St Patrick's Day parade reading: 'England, get out of Ireland'.
A picture showing Ms McDonald walking in the parade was tweeted on the Sinn Féin twitter account.
Tánaiste Simon Coveney tweeted: "MaryLou McDonald, this is NOT leadership - it’s offensive, divisive and an embarrassment".
He went on: "Grow up...This is NOT Ireland in 2019! We are better than this!"
Sinn Féin stood by the banner today, and renewed the party's and Ms McDonald's call for an all-Ireland forum on Irish unity.
Brexit, and the prospect of a hard border on the island of Ireland, has given fresh impetus to calls for a vote on a united Ireland.
Sinn Féin activists gathered in Dublin last month to discuss the campaign for Irish unity and what they say is a “growing demand for a unity poll”.
MaryLou McDonald has challenged the Government to convene an Irish unity forum and said unionists should start planning for “all eventualities”.
Speaking last month, she said: “Obviously, our unionist brothers and sisters need to be part of planning a new Ireland...Their first option, of course, is to maintain the union with Britain and we respect that, but...they need to start now planning for all eventualities and unionism needs a Plan B.”
Ms McDonald claimed that the growing likelihood of a no-deal Brexit has pushed the idea of Irish reunification to the forefront of politics.
She said: “The Good Friday Agreement provides a route to remove the border once and for all. Regardless of Brexit, there will be a unity referendum.
“In our time we now have an opportunity denied to generations – a peaceful and democratic route to Irish unity; to build a new and united Ireland.
“There are those who believe Irish unity is a pipe dream...Some don’t yet appreciate the huge opportunity that Irish unity can present for all of us socially and economically."