The Taoiseach Leo Varadkar has told Egyptian President Abdel Fattah Al-Sisi that he is disappointed at the delay in Ibrahim Halawa's verdict.
In a 25-minute call this evening, President Al-Sisi promised the Taoiseach that the matter would be resolved "swiftly" as soon as a verdict is given.
The Taoiseach also made it clear to the Egyptian President that his priority was to secure the return of Mr Halawa to Ireland as soon as possible.
However, President Al-Sisi emphasised that his Government could not interfere in his country's judicial process.
Both leaders said they look forward to bringing the matter to "an early and satisfactory conclusion".
A statement from Ibrahim Halawa's solicitor, Darragh Mackin, on behalf of Mr Halawa's family has said the decision to adjourn the trial again came "as a huge disappointment" as they expected today's hearing "to be the conclusion of the proceedings".
Mr Mackin said: "Today’s news is truly devastating for our client and his family. Regrettably, this is not the first time the case has been due to conclude when a last minute - unexpected and unjustified decision - is taken to delay the case further.
"We are now four years on, with each day and each false dawn having a hugely significant mental and physical impact on our client’s health. It is not known when this case will ever end.
"Such irrational and unpredictable decisions cannot be allowed to continue, and in particular when they operate in a vacuum of lawfulness depriving our client of his basic rights."
Somaia Halawa, Ibrahim's sister, said: "It is truly upsetting and heart-breaking to constantly keep having our expectations and hopes shattered into a million pieces. It is not just Ibrahim’s life that is being played around with but also the entire family’s life.
"We would ask that our family are allowed some time to ourselves during this difficult period."
Minister Zappone has said Ibrahim Halawa's verdict has been postponed.
"I share the deep disappointment felt by the family of Ibrahim Halawa following the postponement of a verdict," she said.
"Ibrahim and his family are in my thoughts and prayers during this enormously difficult time.
"As Ibrahim's local TD, I remain in continuous contact with the family, his legal team as well as government colleagues. This is a very difficult consular case for the Department of Foreign Affairs and the officials working behind the scenes have my full support.
"Ireland has respected the legal process and we expect it to deliver.
"At a time when hopes are high this further delay is very frustrating. Nevertheless we must continue to put in place the supports necessary to ensure Ibrahim's health and well-being when he is allowed home to be reunited with his loved ones."
He will have to wait another three weeks for the verdict in a trial over Muslim Brotherhood protests in Cairo in 2013, his lawyers have said.
The judgment has been put back until September 18.
Mr Halawa's lawyer, Darragh Mackin of KRW Law, a human rights law firm based in Belfast, said the latest delay was "horrific".
Taoiseach Leo Varadkar has scheduled a phone call with Egyptian president Abdel Fattah el-Sisi for Monday night in a bid to get further guarantees on Mr Halawa's repatriation.
The Egyptian leader previously refused to interfere in the trial following repeated representations from Dublin but said Mr Halawa could be released once a verdict is delivered.
Hearings in the mass trial involving Mr Halawa and 493 others have been adjourned and delayed numerous times over the past four years. The prosecution case ended last month.
No specific evidence was produced relating to Mr Halawa, KRW Law have said.
Along with scores of others he is accused of murders, bombing, possession of firearms and explosives, arson, violence against police and desecration of Al Fatah Mosque.
He has been tortured and gone on hunger strikes during his imprisonment.
A verdict is expected today in the trial of Dublin man Ibrahim Halawa.
The 21-year-old has been in jail in Egypt for the past four years after being arrested during a political protest.
The verdicts of around 500 other defendants are also expected to be announced.
Colm O'Gorman from Amnesty International Ireland has said the outcomes of mass trials like this are very unpredictable.
Thoughts very much with Ibrahim & the Halawa family today. Verdict due in coming hours. After 4 years, there is finally hope. #FreeIbrahim— Colm O'Gorman 🏳️⚧️🏳️🌈 (@Colmogorman) August 28, 2017
"In many mass trails involving hundreds of defendants, we've also seen mass sentences handed down sometimes mass life sentences and indeed mass death sentences," he said.
"It's going to be a very nervous time for Ibrahim's family, friends and supporters."
Ahead of today's verdict, Ibrahim's sister Nosaybathanks those who have been supporting her brother.
"Hopefully we'll hear good news but I want to thank all of the people that have been supporting us, without their support we wouldn't be at this level," she said.