While the identities of the 20 journalists were not revealed by the Egyptian prosecutor, it is believed that Australian Peter Greste, and his two colleagues, dual Egyptian-Canadian citizen Mohamed Fadel Fahmy and Egyptian Baher Mohamed, are among those facing trial.

The three were arrested on December 29 in Cairo’s Marriott Hotel, where the broadcaster had relocated its offices in the face of increasing government criticism of its operations following the downfall of the Muslim Brotherhood-backed president Mohamed Mursi on July 3 last year.

All three vehemently deny the charges, with Mr Greste saying their arrest followed a "relatively uncontroversial" reporting assignment.

The prosecutor announced the Australian, two Britons and a Dutchwoman would also face trial for aiding 16 Egyptians belonging to a "terrorist organisation", widely believed to refer to the Muslim Brotherhood.

After a months-long security crackdown, where many thousands of Brotherhood members and supporters were arrested and at least 1000 were killed, the Egyptian Government designated the Muslim Brotherhood a terrorist organisation on December 25.

It came amid a worsening security situation throughout Egypt, with a series of bombings in Cairo, Mansoura and the restive Sinai province placing the state on high alert for terrorist attacks.

And although the Sinai-based, al-Qaeda inspired militia group Ansar Beit al-Maqdis, or Helpers of Jerusalem, has claimed responsibility for much of the carnage, the Egyptian government has repeatedly blamed the Brotherhood. It in turn has denied any links to the attacks, which have mainly targeted police stations and security installations.

“The fact that we were arrested for what seems to be a set of relatively uncontroversial stories tells us a lot about what counts as ‘normal’ and what is dangerous in post revolutionary Egypt,” Mr Greste wrote in one of two letters smuggled from his cell in the Tora Prison in Cairo.

"The state will not tolerate hearing from the Muslim Brotherhood or any other critical voices," he wrote. "The prisons are overflowing with anyone who opposes or challenges the government."

According to a statement released by the prosecution on Wednesday: “Investigations showed the defendants created a media network headed by an Egyptian-Canadian Muslim Brotherhood member that has specialised in creating video scenes contrary to reality and aired them through Qatari al-Jazeera English to distort Egypt's international reputation.”

Mohamed Fadel Fahmy's brother, Adel Fahmy, denied his brother was a member of the Brotherhood, and told CNN that his brother's lawyer had confirmed he was among the defendants named in a statement by Egyptian prosecutors.

Other charges levelled at the journalists included "disturbing public peace, instilling terror, harming the general interests of the country, possessing broadcast equipment without permit, possessing and disseminating images contrary to the truth".

The announcement of the charges – sure to be a devastating blow to those in prison and those who have been campaigning for the journalists’ freedom – came as al-Jazeera, along with Mr Greste’s parents Lois and Juris Greste, intensified their efforts to secure the release of the men.

Along with Mr Greste, Mr Fahmy and Mr Mohamed, two other journalists from sister channels al-Jazeera Arabic and al-Jazeera Mubasher Misr - Abdullah al-Shami and Mohamed Bader – have been in detention for five months.

Al-Jazeera is thought to be struggling to identify the 20 facing charges, and it is believed some may face trial in absentia.

The prosecution’s move made it difficult for other foreign journalists to operate in Egypt, warned Khaled Mansour, the head of the human rights group Egyptian Initiative for Personal Rights.

"I have a very strong concern now for journalists, especially foreign journalists, who are trying very hard to create a balanced picture of what is going on in this country," Mr Mansour told The Guardian. "This will really have a very chilling effect on the work of journalists."

As Mr Greste points out in his second letter smuggled from prison: “To defend the revolution Egyptians have just passed a fiercely liberal constitution that, amongst other things, explicitly … [protects] freedom of speech.

“Article 11,” he notes, “even expressly protects journalists from imprisonment for crimes committed through publishing or broadcast.”

The Committee to Protect Journalists also voiced its concern over the charges.

"None of the governments who have come to power in Egypt since the 2011 uprising have delivered on their promises to respect freedom of the press," said Sherif Mansour, CPJ's Middle East and North Africa Coordinator.

"It is difficult to see how the country could achieve anything like democracy when it is one of the most dangerous places on earth for journalists to do their jobs."