Sinn Féin leader, Mary Lou McDonald, has said Britain has legal obligations to Ireland despite their impending departure from the European Union.
Her comments come as an influential backbench Conservative MP, Graham Brady indicated he would back a deal if a suitable compromise on the backstop could be found.
She was speaking at a memorial for women in the Magdalene Laundries in Glasnevin Cemetery in Dublin.
Ms McDonald said a backstop arrangement to secure free movement over the border is essential.
She said: "The fact is that the British State has obligations to Ireland in international law as per the Good Friday Agreement.
"Those obligations have to be held firm, so we have argued all along that there is no such thing as a good Brexit. Our job is to protect Irish interests and the backstop is the absolute bottom line."