Islamist protesters barricade themselves inside the al-Fatah mosque. Pic: AP.

One of the four Irish citizens trapped inside a mosque in Cairo has said the protestors have "personally threatened to slaughter" her if they see her.

The four are among hundreds of people trapped in the mosque fearful they will be attacked if they leave.

The Department of Foreign Affairs say their family are in continous contact with Egyptian authorities and security forces in relation to their safety and well-being.

The three women and a teenager are children of Hussein Halawa – the Imam of Ireland’s biggest mosque in Dublin.

The four siblings, who are on holiday in Egypt, sought refuge in the mosque after 80 people were killed during violent clashes between supporters of ousted president Mohammed Morsi and the security forces in Cairo yesterday.

Omaima Halawa, 21, who is with her two sisters Somaia, 27, and Fatima, 23, as well as their younger brother Ibrihim, 17, described the scene in Cairo as very frightening.

“We are surrounded in the mosque both inside and outside,” she told RTÉ.

“The security forces broke in and threw tear gas at us.”

She said they had been warned they could be shot if they tried to leave.

“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.”

An angry crowd greets an Islamist supporter of the Muslim Brotherhood as he is escorted by Egyptian security forces out of the al-Fatah mosque. Pic: AP.

Ms Halawa said conditions inside the mosque are austere with no food, a lack of clean water, dozens of injured people and few medical supplies.

“There was a group of ladies who left. When they left they were attacked and taken,” she said.

“We are not safe.”

Ms Halawa was taking part in a demonstration when violence forced them into the mosque at about 7pm last night.

Her family is now too scared to leave without help and assurances from a diplomat. Thugs outside the mosque have threatened to kill her if she leaves the building, Mrs Halawa said.

Ms Halawa, who is a final year student at Blanchardstown Institute of Technology, said the Irish authorities had been in contact.

They had travelled to Egypt with their mother for a holiday earlier this summer. Their father remained in Dublin.

From the family home at Firhouse in the south of the city, another sister Nasaybi said they were enduring a terrible ordeal.

Egyptian security forces escort an Islamist supporter of the Muslim Brotherhood out of the al-Fatah mosque. Pic: AP.

She said: “We are really worried. We do not know how to help them. We are just trying to support them by calling and giving them some hope that they will get home safely.”

A spokesman for the Department of Foreign Affairs said embassy staff had been in contact with the group and were working closely with the authorities in Cairo.

He said: “We can confirm we have been in touch with the group. We can also confirm that embassy staff have been in touch with the authorities in Egypt.”

Egyptian security forces escort an Islamist supporter of the Muslim Brotherhood out of the al-Fatah mosque. Pic: AP.

Later today hundreds of people are expected to take part in a solidarity protest at the Egyptian embassy in Dublin.

The rally, hosted by the Irish Anti War Movement, hopes to put pressure on the Irish Government to condemn the massacre of civilians in Cairo.