Al Jazeera journalist Abdullah El-Shamy, who has been on hunger strike since January, was granted release on Monday by Egypt's general prosecutor for health reasons.
Twelve other detainees were also released for medical reasons, according to a statement by the general prosecution. The names of the released detainees are: Moaz Arafa, Ibrahim El-Shafei, Mahmoud Ahmed, Mahmoud Salam, Mohamed El-Ashry, Abdel-Kader Hamady, Khaled Abdel-Razek, Mahmoud El-Shazly, Moustafa Gomaa, Yasser Mahmoud Abdel-Attif, Mohamed El-Sawy and Yehya Hasan.
Last week, an Egyptian court renewed the detention of El-Shamy for 45 days – despite reports that he has lost almost a third of his body weight and is in poor health as a result of the hunger strike.
El-Shamy has been held for almost 10 months after being arrested on 14 August, when police dispersed major protest camps in Cairo by supporters of ousted Islamist president Mohamed Morsi, leaving hundreds killed.
He faces allegations that include inciting violence, rioting, and disrupting public order. He has yet to be referred to trial.
El-Shamy's lawyer said he appeared to be suffering "severe fatigue" during last week's hearing, held at a courthouse in Torah Prison on the southern outskirts of Cairo.
The 30 June fact-finding committee, commissioned by former interim president Adly Mansour, said on 5 June the jailed journalist was in good health, claiming he had ended his hunger strike.
El-Shamy's family, who visited him in a highly-guarded security prison on 4 June said he had told them he "had eaten no food and that no food had entered his cell at any time," Al Jazeera English's website reported.
The family has repeatedly warned that the detained journalist's health is in danger.
Three other Al Jazeera journalists – including an Australian national – who work for the network's English-language channel have been held in Egypt since December 2013.
They face trial over allegations of airing false news and aiding or joining the Muslim Brotherhood movement, designated by authorities as a terrorist group.
Al Jazeera strongly dismisses the charges against all of its journalists and continues to call for their immediate release.