Four Irish siblings caught up in the violence in Cairo are being held by Egyptian authorities, their family said.
Omaima Halawa, 20, her two sisters Fatima, 22, Somaia, 27, and their younger brother Ibrihim, 17, were among hundreds of people cleared out of the Al Fateh mosque when security forces stormed the building yesterday.
Their father Sheikh Hussein Halawa is the Imam of Ireland's largest mosque in Dublin.
At the family home in Firhouse, south Dublin, another sister Nasaybi Halawa said the four were being held at one of Cairo's jails.
"The latest we know is that they are in one of the jails in Cairo. But we do not know if they are all together or whether they have been separated - boys and girls," she said.
They are concerned that teenage Ibrihim, who has just completed his Leaving Certificate, may have been separated from his sisters.
Ms Halawa added: "It is very hard. We just know that they are being held. We don't know if they have food supplies or water, whether they have slept or whether or not they will be released. If they are not released before 7pm then they will have to wait until another day because of the curfew in Cairo which prevents people walking on the streets after 7pm.
"The security forces surrounded them in the mosque for 12 hours and didn't give them any food or supplies and that was while the world was watching on television. Now, when they have them and no one can see them, what are they going to do? We are worried - are they safe, were they beaten or injured while leaving the mosque? We just don't know.
"It is very difficult. This is the hardest time in our lives."
Tear gas was fired and heavy gunfire was heard before the mosque, in the Ramses area of Cairo, was cleared.
The siblings have not been able to contact their family directly. It is understood their mobile phones have been seized.
Ms Halawa said her mother, who is staying with relatives in Egypt, had been contacted by a woman who had seen Omaima in one of the detention centres.
The Irish Department of Foreign Affairs has confirmed they are working closely with counterparts in Egypt in a bid to secure the safe release of the family.
The Halawas had travelled to Egypt earlier this summer for a holiday and were joined by their mother a fortnight ago.
They were forced to seek sanctuary in the Al Fateh mosque on Friday after violent clashes between supporters of ousted president Mohammed Morsi and the security forces killed around 80 people. More than 800 people have died in the carnage that has followed a military crackdown over the past four days.
Ms Halawa said: "They thought the mosque is a holy place and that they would be safe there. They phoned my father and told him they were in the mosque and that they were going to pray and afterwards would leave. But, by the time prayer time had finished they were surrounded."
Speaking from inside the mosque yesterday Omaima Halawa, a final-year student at Blanchardstown Institute of Technology, told of her fears and said she did not feel safe enough to leave the building without a diplomatic escort.
"We are surrounded in the mosque both inside and outside," she told Irish national broadcaster RTE.
"The security forces broke in and threw tear gas at us."
She also claimed "thugs" outside the mosque had threatened to kill her if she left the building and said others who had tried to flee were "taken".
She said: "We want a safe passage out for the four of us. I do not trust (security forces) or the thugs.
"They have personally threatened to slaughter me when they see me."