Amnesty International has repeated its warning of a likely legal challenge if Northern Ireland is left as the only part of the UK without marriage rights for same-sex couples.

The warning came as a motion in the Northern Ireland Assembly supporting same-sex marriage was set for defeat after the Democratic Unionist Party (DUP) lodged a Petition of Concern, meaning the proposal can only pass if a majority of both unionists and nationalists support it.

Patrick Corrigan, Amnesty International's Northern Ireland Programme Director, 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. This means that marriage should be available to same-sex couples in Northern Ireland, just as it is now in England and Wales and will shortly be in Scotland.

"Equally, the right to adopt, for instance, should be available without distinction based on sexual orientation or gender identity. Recently, that right to non-discrimination for people in Northern Ireland was secured through the courts rather than around the Executive table.

"Sadly, it appears that some politicians prefer to continue to abdicate their responsibilities, leaving it instead to judges to do the right thing.

"With politicians continuing to block equality, it is now inevitable that same-sex couples in Northern Ireland will take a legal challenge on the basis of inferior treatment with regards to the right to marry and found a family."