Image copyright PA Image caption First Minister Arlene Foster said she would deploy a petition of concern to block same-sex marriage

Arlene Foster is "childish" and "disingenuous" for saying online abuse is partly why the DUP is unlikely to change its view on same-sex marriage, Alliance leader Naomi Long has said.

Northern Ireland is the only part of the UK where gay marriage is not legal.

Mrs Foster said the DUP would use a petition of concern to block any change to the law over the next five years.

A petition of concern places the requirement of a cross-community majority on a motion in the assembly.

Last year, a majority of MLAs voted in favour of same-sex marriage. but the motion was blocked by a DUP when it deployed the petition.

Image caption Alliance Party leader Naomi Long said the DUP are "abusing" petitions of concern

What is a petition of concern?

The measure was designed as a way to safeguard minority rights in Northern Ireland's power-sharing assembly.

If a petition of concern is presented to the assembly speaker, any motion or amendment will need cross-community support.

In such cases, a vote on proposed legislation will only pass if supported by a weighted majority (60%) of members voting, including at least 40% of each of the nationalist and unionist designations present and voting.

Effectively this means that, provided enough MLAs from a particular community agree, that community can exercise a veto over the assembly's decisions.

A valid petition requires the signatures of 30 MLAs. The DUP has 38 seats, including the speaker.

Mrs Foster insisted her party was not anti-gay but said that "very, very vicious" online abuse from LGBT activists demanding a law change made it less likely the DUP would support the move.

"If activists want to have a conversation about where they are coming from, do they seriously think they are going to influence me by sending me abuse?

"No, they are not going to influence me by sending me abuse - in fact, they are going to send me in the opposite direction and people need to reflect on that."

Alliance leader Naomi Long criticised Mrs Foster for "blaming online trolls" for the DUP's position on same-sex marriage.

"It is not just childish and ill-fitting for the office that she holds, but actually is disingenuous because her party has, at every opportunity, sought to block any progress for the LGBT community in Northern Ireland."

Image copyright Getty Images

On Thursday, Mrs Foster also questioned why the DUP would "give away" the petition of concern when the party feels "so strongly about the definition of marriage".

Mrs Long told the BBC that the DUP were "abusing the petition of concern to overturn what would be a democratic majority".

"By all means, if they don't agree with equal marriage they can vote against it.

"But I would hope that in a more mature democracy, that we could have seen some progress in terms of limiting the use, if not getting completely rid, of petitions of concern as a mechanism.

"So that we rely on simple democratic principle."

Sinn Féin MLA Sean Lynch said that same-sex marriage was raised at the Northern Ireland Executive on Thursday but was "blocked" by the DUP.

"This is first and foremost an equality issue and Sinn Féin is committed to seeing marriage equality extended across the island," he said.