A group of journalists from around the globe launched an online campaign on Monday calling for the release of three Al-Jazeera journalists who have been detained in Egypt for over three months.

The viral campaign on Twitter marked 100 days that Peter Greste, Fahmy Fadel and Baher Mohamed have been in prison since being arrested last December on charges of aiding a terrorist organisation – a reference to the outlawed Muslim Brotherhood.

They are currently facing a trial at a Cairo criminal court along with 17 other defendants.

The campaign on Monday – under the hashtag #FreeAJstaff – featured journalists from the BBC and various Al-Jazeera channels, who posted photos on Twitter with their mouths covered with tape while holding banners reading "Free AJStaff" and "Journalism is not crime".

Hundreds of BBC journalists and reporters gathered outside the BBC building in London for a minute of silence in solidarity with the Al-Jazeera reporters imprisoned in Egypt as well as other detained journalists around the world. 

The BBC staff held photos of Greste, Fadel and Mohamed as well Al-Jazeera Arabic correspondent Abdullah El-Shamy, who was arrested during the violent dispersal of the Rabaa Al-Adaweya protest camp in August and has not yet been charged. 

El-Shamy has been on a hunger strike for 76 days to object his detention without charge, according to his family, who have called for his release. 

Al-Jazeera's Cairo offices have been closed down since 3 July, when they were raided by security forces in the immediate aftermath of the ouster of President Mohamed Morsi, who hails from the Brotherhood.

The only Al-Jazeera-affiliated channel to have been banned by court order is Al-Jazeera Mubasher Misr.

Monday's efforts are not the first calling for the release of Greste, Fadel and Fahmy, whose detention has sparked an international outcry and led to condemnation by human rights groups and media organisations.

They were denied bail on 30 March and their trial has been adjourned to 10 April.