An Irish citizen facing the death penalty has entered his fifth year of incarceration in Egypt without being brought to trial, a milestone that has angered family members and rights groups who have campaigned for his release.

Friends and family gathered outside the Egyptian embassy in Dublin on Thursday, marking four years of Ibrahim Halawa's imprisonment.

Halawa, now 21, was just 17 years old when he was arrested by Egyptian security forces in Cairo in August 2013.

He was held as part of a crackdown on protesters rallying against the government of Abdel Fattah El Sisi, which was then newly in power.

He has attended several mass trials with hundreds of prisoners, but the court date has been postponed more than 30 times.

"Ibrahim and hundreds of others were arrested, and jointly accused of responsibility for violence," a statement by human rights organisation Reprieve said.

"Though he was just 17 - a juvenile - at the time of his arrest, Ibrahim faces the death penalty in a mass trial of 494 people."

READ MORE: A letter to my brother in Egyptian prison

Halawa's health has deteriorated over the years, with the young man protesting against his detention with several hunger strikes.

"Today we say that four years is too much," said his sister Somaia Halawa. "Four years in an Egyptian prison, four years of a mass trial, four years of hope of freedom that never came true, four years of waiting.

"One day is too much, four years is torture. We miss our brother desperately."

'Shameful'

Somaia, her two sisters Fatima and Omaima, and Ibrahim had taken refuge in the Fath mosque in Cairo before they were all arrested. The three sisters were released on bail three months later.

"Four years is too long for someone who is innocent," Somaia said. "Four years is too much for our brother, the 17-year-old boy who has become a man locked away from the world, from his family, from his friends."

READ MORE: Egypt jails scores for life over 2011 protests

The director of Reprieve, Maya Foa, condemned the European Union's support of Egypt's judiciary as "shameful" while "a European juvenile like Ibrahim is allowed to languish in hellish conditions".

"Now more than ever, the entire international community must urge the Egyptian government to end the abuses perpetrated against Ibrahim and many others," Foa said.

Meanwhile, the Irish Minister of Foreign Affairs Simon Coveney said his government was determined to see the release of Halawa.

"I want to reaffirm my determination and that of the Irish government to seeing this young man released from prison in Egypt and returned to his family in Dublin so that he can resume his life and his studies," Coveney said.

Some expressed their hopes for Halawa's return on social media:

On #ALevelresultsday2017 spare a thought for #FreeIbrahim who was arrested and detained at 17yr, starts his 4th year in #Egyptian jail today — Darragh Mackin (@darraghmackin) August 17, 2017

Today marks Ibrahim's 4th year in unfair imprisonment, we cannot stand for it any longer. #4yearstoolong #freeibrahim pic.twitter.com/wwK1u3ETCW — IT Carlow SU (@ITCarlowSU) August 17, 2017

Today marks 4 years since Ibrahim Halawa's arrest. When will he be home? #FreeIbrahim pic.twitter.com/Fb7e8f2fZZ — Bríd McGrath (@BCCMcGrath) August 17, 2017

Ibrahim Halawa detained for 4 years today. He and other prisoners treated shamefully. He should be immediately released. #FreeIbrahim — Joe Higgins (@JoeHigginsSP) August 17, 2017

today marks four years since ibrahim Halawa had been imprisioned in egypt #4YearsTooLong #FreeIbrahim pic.twitter.com/fBAm3dwtkY — TCD Students' Union (@tcdsu) August 17, 2017

4 years of your life in jail without access to lawyers, med treatment or a fair trial goes against every principle of justice. #freeibrahim https://t.co/XDQTrgnVG9 — Carly Bailey-SocDems (@CarlyBee25) August 17, 2017