Dublin's Ibrahim Halawa remembered as he spends 20th birthday in Egypt prison

Thousands of well-wishers have sent messages to an Irish teenager potentially facing execution in Egypt as he prepares to spend his third birthday behind bars.

Ibrahim Halawa is said to have endured "torture and inhumane treatment" - including regular beatings - while in detention at the notorious Wadi Natrun prison, where guards are alleged to have used electricity and even "crucifixion" on inmates.

The Dubliner was just 17 years old when in August 2013 he was arrested by the Egyptian army as he took refuge in a Cairo mosque while Muslim Brotherhood protesters staged a "day of rage" outside.

Demonstrators took to the streets after their elected leader, Mohamed Morsi, was ousted from power in a military "coup", leading to a crackdown ordered by army chief Abdel Fattah al-Sisi, now the country's president.

It is feared Halawa, who was on his summer holiday in the Egyptian capital when violence flared, will face the death penalty when a mass trial of 494 alleged dissenters resumes on Tuesday. The legal proceedings have been repeatedly delayed since 2013.

The campaign group claim the teenager has described "experimental torture techniques" to his family in messages sent from jail, where he will see in his 20th birthday on Sunday.

A birthday card organised by human rights group Reprieve and signed by over 8,000 people was presented to the Egyptian embassy in London, although officials refused to accept it when it was delivered by hand last night.

Maya Foa, director of Reprieve's death penalty team, said: "It is a total disgrace that Ibrahim Halawa is spending a third birthday behind bars in Egypt, awaiting a mass trial that makes a mockery of justice.

"It is plain to see that the Egyptian courts offer no hope of justice - just the real threat of a death sentence handed down en masse. The Irish government and other countries that are closely allied with Egypt - including the UK - must urgently push for Ibrahim's release, before it's too late."

According to Reprieve the Egyptian government has sentenced nearly 600 people to death in the year, with most alleged crimes linked to political protest.

Halawa's case was raised in a joint motion for resolution on the death penalty due to be discussed in the European Parliament next week.

Sean Kelly, MEP for Ireland South, has given his "full support" to Halawa.

The Egyptian embassy has been approached for comment.

Early last month Halawa's legal team, made up of lawyers from Ireland and Britain, wrote to prime minister David Cameron to raise his case with president Abdelfattah Sisi of Egypt during his visit to London.

They set out the "long list" of violations of the youngster's rights and the incompatibility of any mass trial with "the most basic judicial standards of fairness".

Halawa's Belfast-based solicitor Darragh Mackin said they had received no indication of whether Mr Cameron raised his client's situation with the Egyptian leader.

Should the trial go ahead the hundreds of defendants would be tried under similar rules to the "joint enterprise" system in the UK, except on a vast scale.

"Individuals are not going to get the chance to represent their case. They are effectively charged under joint enterprise," he said.

Hawala's mother is understood to have flown to the country to visit him in jail, although her only contact with her son will be through a narrow gap between two cages, Mr Mackin said.