The Tánaiste has raised concerns about the "citizenship and identity provisions" of the Good Friday Agreement after a Northern Irish woman lost a challenge by the British Home Office on its ruling that she is British by birth.

Emma DeSouza, from Magherafelt, Co Derry, accused the British government of failing to honour the spirit of a commitment in the Good Friday Agreement that people from the region could identify as British, Irish, or both.

Tánaiste and Minister for Foreign Affairs Simon Coveney tweeted a response to the ruling, saying that citizenship and identity provisions are "critical" to the Good Friday Agreement.

He said the UK government has pledged to review rules around citizenship and deliver a long-term solution consistent with the Good Friday Agreement.

"An outcome is urgently needed and I will raise this again with Secretary of State for NI tomorrow," he said.

Ms DeSouza has vowed to continue her legal battle.

Ms DeSouza, who insists she is Irish and has never been British, claimed the British Home Office's "hard-line" approach was an attempt to restrict access to EU entitlements in Northern Ireland post-Brexit.

The Home Office won an appeal against an immigration tribunal case that had originally upheld Ms DeSouza's right to declare herself as Irish, without first renouncing British citizenship.

The long-running wrangle centres on her application for a residence card for her US-born husband Jake.

After the Upper Tribunal ruling today, Ms DeSouza, pledged to take her case to the Court of Appeal in Belfast.

"After four years it's safe to say we won't be lying down anytime soon," she said.

Speaking on RTÉ's Drivetime, she said that being Irish is "simply who I am" and said she is "devastated and disappointed" by today's decision.

"The core of this is the fact that I am not a British citizen. I haven't held a British passport, I haven't accepted British citizenship, and I understood that the Good Friday Agreement gave us an explicit right to identify and be accepted as Irish or British or both. I'm Irish. It wasn't a choice or a decision, it's simply who I am."

Ms DeSouza said the UK government has failed to adequetely legislate essential provisions of the Good Friday Agreement into domestic UK law.

She described identity in Northern Ireland as a "personal, complex and sensitive" that was central to the Good Friday Agreement.

She said today's decision "sets a precedent" and that she believes it is a rewriting of the Good Friday Agreement.

"If it starts with this, what will be the next provision of the Good Friday Agreement that will be changed by the British government? I think there are some serious things at play here that go much further than the immigration status of my husband and much further than me renouncing British citizenship."

In 2015, Ms DeSouza made the residence card application identifying herself as an Irish citizen.

The Home Office rejected it on the grounds that it considered Ms DeSouza a British citizen.

Officials told her she could either reapply identifying herself as British, or renounce her UK citizenship and reapply as an Irish citizen.

The Co Derry woman argued that she never considered herself British, so how could she renounce citizenship she never had.

During the stand-off, the Home Office retained her husband's passport for two years - a move that forced him to quit a music band, as he could not tour, and prevented him from attending his grandmother's funeral in the US.

Ms DeSouza took a legal challenge against the Home Office and won, with a judge at a First Tier Immigration Tribunal ruling in 2017 that she was an "Irish national only who has only ever been such".

The Home Office appealed against that decision at an Upper Tribunal hearing earlier this year. Those judges found in its favour.

British government lawyers argued that the British Nationality Act 1981 was the relevant legislation - not law flowing from the Good Friday Agreement.

Citizenship + Identity provisions critical to the GFA. UK Govt has pledged to review rules around citizenship and deliver a long term solution consistent with GFA. An outcome is urgently needed and I will raise this again with Secretary of State for NI tomorrow @EmmandJDeSouza — Simon Coveney (@simoncoveney) October 14, 2019

In a statement, a Department of Foreign Affairs spokesman noted comments from former UK prime minister Theresa May last February to review the citizenship and identity issues.

"The (Irish) Government is continuing to actively seek the outcome of that review with the new British Government and the Tanaiste (Mr Coveney) will be raising this again with the Secretary of State for Northern Ireland when they next meet," he added.

Ms DeSouza has attracted cross-community support for her challenge.

At a press event in Belfast today she was joined by Sinn Féin senator Niall Ó Donnghaile, Alliance deputy leader Stephen Farry, SDLP MLA Claire Hanna and former Ulster Unionist Party leader Mike Nesbitt. Mr Nesbitt said he was attending in a personal capacity.

Ms DeSouza said she and her husband were not politically active until their application was rejected.

"We have had to become active and been forced into a situation where we have to keep every day fighting for this right under the Good Friday Agreement," she said.

"It's certainly not somewhere where we could have seen ourselves going four years ago when we got married."

Sinn Féin leader Mary Lou McDonald said: "This decision from the court today in the Emma de Souza case is a disgracefully retrograde step.

"The Good Friday Agreement is crystal clear on this in terms of citizenship. Emma De Souza is an Irish citizen and it is disgraceful that she should have to go to court to prove it."