Sinn Féin had set out demands on same-sex marriage as part of attempts to reach a fresh power-sharing deal in Northern Ireland.

Assembly elections were held earlier this month in Northern Ireland after the collapse of the previous government, with Democratic Unionist Party losing ground after a corruption scandal.

The anti-gay marriage DUP, which is still the largest party with a reduced majority, had previously used peace process powers known as ‘petitions of concern’ to block same-sex marriage.

Under the Good Friday Agreement, second-largest party Sinn Féin must form a new power-sharing government with the DUP – but the two parties failed to reach a deal by the deadline this afternoon.

The talks collapsed after Sinn Féin set out a number of red lines, including progress on equal marriage.

The party has since alleged that the DUP refused to budge on the issue.

Sinn Féin President Gerry Adams said: “The DUP’s approach thus far has been to engage in a minimalist way on all of the key issues, including legacy issues – an Irish-language act, a bill of rights and marriage equality.

“They have been reinforced in this by the British government’s stance. This is unacceptable and a matter of grave concern.”

Speaking at a press conference today after the collapse of talks, Sinn Féin MLA Michelle O’Neill said: “Unfortunately the DUP maintained their position in relation to blocking equality and delivering equality for citizens. That is a problem.

“We, over the course of today, have a range of meetings with the other parties. We continue to engage. We do need to make the institutions work, but they can only work on the basis of equality, respect and integrity at their course.”

The DUP’s Arlene Foster, an opponent of LGBT rights, insisted: “These talks failed because there wasn’t a recognition of everyone’s mandates and there wasn’t a spirit of compromise to get back into the executive.”

She insisted: “The DUP stands ready to continue to discuss how we can secure new arrangements for Northern Ireland.”

Ms Foster previously reaffirmed plans to continue employing powers to block any future marriage legislation. She recently defended her actions by insisting gay people don’t really want to get married anyway.

She said: “This suggestion that every single person who’s a homosexual wants to change the definition of marriage is actually wrong.

“I know plenty of people in that community who don’t want to see marriage redefined and are quite content to live in partnership… it’s all become a bit of a storm in a teacup.”

The UK government has extended the deadline for the talks.

The Secretary of State for Northern Ireland, Rt Hon James Brokenshire MP, branded the collapse of talks “extremely disappointing”.

He said: “We now have a short window of opportunity to resolve outstanding issues and for an Executive to be formed.

“Everyone owes it to the people of Northern Ireland to grasp that and provide the political leadership and the stability they want.”