A group of UN human rights experts have expressed "grave concern" for the welfare of Irish woman Lisa Smith and her child.
Ms Smith, who travelled to Syria three years ago to live in the so-called Islamic State is believed to be in Turkey.
In a statement issued through the UN's Office of the High Commissioner on Human Rights, the experts expressed fear that the Dundalk woman "may face ill-treatment in custody".
They called for her to be given consular assistance and be protected from abuse and expressed concern about her and her daughter's mental and physical health.
"The vulnerability of this infant is particularly worrying and there is a compelling obligation to protect her well-being in accordance with the Convention on the Rights of the Child to which Turkey and Ireland are both parties," the experts said in their statement.
The UN group, which includes rapporteurs on torture, arbitrary detention and violence against women, called for the basis of Ms Smith's detention in Turkey to be clarified and for access to legal counsel to be given to her.
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The Department of Foreign Affairs confirmed it is in contact with the office of the relevant UN human rights mandate holders in respect of their appeal on the Smith case.
A spokesperson said Ireland is fully conscious of its obligations under international law, including international human rights law.
Given that this is an ongoing consular case, the spokesperson said there was no further comment.
Among those who signed the UN OHCHR statement was Fionnuala Ní Aoláin, Special Rapporteur on the promotion and protection of human rights and fundamental freedoms while countering terrorism.
She said Ms Smith is formally in the custody of Turkish authorities and "not a non-state actor group".
Ms Ni Aoláin said the UN had concerns that women, including Ms Smith, would be subject to interrogation in Turkey without legal advice and intervention of consular assistance.
She said: "All of those individuals would be at a great vulnerability including the young child involved - not least because we couldn't ascertain the extent of the injuries or harms that might have occurred to them during the course of their detention and their bombardment."
However, she commended both Ireland and Turkey for abiding by their obligations under law and reaching out actively to one another in relation to the Smith case.