Media playback is unsupported on your device Media caption It is the third time in the past 18 months that Stormont has rejected same-sex marriage

The Northern Ireland Assembly has rejected a motion calling for the introduction of same-sex marriage during a debate at Stormont.

A total of 51 assembly members (MLAs) voted against the Sinn Féin motion, while 43 MLAs voted in favour.

It is the third time in the past 18 months that Stormont has rejected same-sex marriage.

Northern Ireland is now the only part of the UK which has not passed a law to introduce same-sex marriage.

The first gay marriages have recently taken place in England and Wales, with Scotland due to follow later this year.

Ahead of the latest Stormont vote, the human rights organisation Amnesty International said Northern Ireland politicians would not be able to block same-sex marriage indefinitely.

The debate, led by Sinn Féin, began on Tuesday with the party insisting this was an equality issue.

The Social Democratic and Labour Party (SDLP) backed the motion which also supported freedom of religion.

The DUP is opposed and tabled a petition of concern ensuring the motion would be blocked under the Northern Ireland Assembly's cross- community voting rules.

The party had argued this was not about equality, nor human rights and said it was opposing the redefinition of marriage.

However, when it came to the vote, the DUP did not need to depend on their veto, as the No camp had a majority of eight over the supporters of same-sex marriage.

All the nationalist MLAs who took part in the vote backed gay marriage, while most unionists rejected it, with only four of them voting in favour.

Alliance Party MLA are designated as "other", as opposed to defining themselves as unionist or nationalist in the assembly.

Their party policy is also in favour of same sex-marriage, but two Alliance MLAs, Judith Cochrane and Trevor Lunn, voted against the motion.

The Ulster Unionist Party voted on conscience grounds and only two UUP MLAs, Michael Copeland and Danny Kinahan, broke the unionist trend and voted in favour.

Both of NI21's MLAs, Basil McCrea and John McCallister, who are designated as unionists, voted to support same-sex marriage.

Jim Allister, leader of the Traditional Unionist Voice voted no while Green Party leader Steven Agnew voted yes.

Patrick Corrigan, director of Amnesty International, said: "Politicians in Northern Ireland who continue to block marriage rights for same-sex couples are like latter-day King Canutes, trying in vain to hold back the tide of equality.

"States may not discriminate with regards to the right to marry and found a family, on the basis of sexual orientation or gender identity.

"That obligation is clear in international law."

The Sinn Féin motion proposed that Stormont introduce legislation similar to other jurisdictions in Britain and Ireland.

The motion comes a day after Catholic bishops in Northern Ireland published an open letter to all MLAs urging them to reject the same-sex marriage motion.

Image caption A rally in favour of same-sex marriage was held in Londonderry on Monday evening

The letter said it undermined the principle of equality by applying it "inappropriately".

The assembly motion said that "other jurisdictions in Britain and Ireland have moved forward with same sex-marriage" and that Stormont should introduce similar legislation.

The motion also said religious institutions should have the freedom to decide whether or not to conduct same-sex marriages.

This was the third attempt to persuade MLAs to back same-sex marriage in Northern Ireland.

A year ago, they rejected a similar motion by 53 votes to 42.

Supporters have stepped up their campaign following the first gay weddings in England and Wales.

Rallies in favour of same-sex marriage were held on Monday evening in Belfast and Londonderry.

As well as the Catholic Church, the Evangelical Alliance made its opposition to the motion clear.