The Foreign Affairs Minister says he is "disappointed" at the further delay of the trial of a Dublin teenager in Eygpt.

19-year-old Ibrahim Halawa has been in custody since he was arrested during protests in the city in 2013.

The trial, due to take place today, has been adjourned until the 4th of October, allegedly because some witnesses didn't attend.

Minister Charlie Flanagan said this latest delay is a source of deep frustration to Ibrahim and his family - and he has pledged to keep working actively to secure his release.

In a statement, Minister Flanagan said, “in my many contacts with my Egyptian counterpart Foreign Minister Sameh Shoukry, I have emphasised the importance of due process in this case and have highlighted the Government’s continued concern regarding the length of time our citizen has spent in detention while awaiting trial.

"I spoke again to Minister Shoukry last Wednesday and strongly reaffirmed the Government’s deep interest in Ibrahim’s welfare," he added.

Sinn Féin MEP Lynn Boylan is in Eygpt and attempted to attend today's hearing, and said she's "devastated" for Ibrahim's family:

Ibrahim's sister, Somaia Halawa, said they are increasingly concerned for his mental and physical health:

Ibrahim was arrested in 2013 in Cairo during protests in the city's al-Fateh mosque against the military-led overthrow of president Mohamed Morsi of the Muslim Brotherhood.

Halawa had just completed his Leaving Cert at the time, and has been held in prison since.

He and his almost 500 co-accused are due to go on trial in relation to charges which include murder, the use of explosives and terrorism. Several other court dates have already passed without Halawa's case being heard.  

Authorities in Egypt have agreed to allow the chairperson of the Oireachtas Foreign Affairs Committee visit the 19-year-old in the coming days.