A local rights group said on Monday that more prisoners, including a prominent female activist, have joined an ongoing hunger strike to protest their detention.
The Arabic Network for Human Rights Information (ANHRI) said in a statement on Monday that Mahienour El-Masry, a human rights activist jailed for breaching a controversial protest law, started a hunger strike on Sunday.
El-Masry, who has been detained since May, is serving a 6-month jail term after her two-year sentence from earlier this year was reduced by an Alexandria court in July.
At least 11 supporters of deposed president Mohamed Morsi arrested amid a sustained clampdown on Islamists have also joined the hunger strike to protest being detained without charges, the Cairo-based rights group said.
The group said the move comes in reaction to "unfair trials" and "noticeably prolonged pre-trial detentions" in cases that it describes as being matters of freedom of expression.
Since the army's ouster of Morsi in July 2013, authorities have mounted a harsh crackdown on Islamists in which thousands have been jailed and hundreds killed or sentenced to death in hurried mass trials.
The campaign has also extended to several youth activists after a law that bans all but police-sanctioned demonstrations was passed late last year.
Last week, Alaa Abdel-Fattah, a well-known activist and blogger who was a figure of the 2011 uprising, began a hunger strike to protest his imprisonment over charges of violating the widely criticised protest law.
In June, an Egyptian court sentenced Abdel-Fattah to 15 years in jail on charges of participating in an illegal protest and assaulting police. He is now being retried due to the sentence being handed out in absentia.
Three other symbols of the 2011 popular revolt that toppled autocrat Hosni Mubarak have announced they will join the open-ended hunger strike if authorities do not do meet the other detainees' demands.
The trio--Ahmed Maher, founder of the April 6 Youth Movement, Mohamed Adel, a prominent April 6 member, and long-time activist Ahmed Douma--was jailed for three years each late last year on similar charges of illegal protesting.
The protest law, passed in November 2012, has heighted fears of a general muzzling of political dissent and was strongly condemned by local and international rights watchdogs as being "highly restrictive" and "draconian."
Authorities say the law is essential to bring about order and stability and ensure the rule of law after the unrest following Morsi's ouster last summer.
A protest is planned later on Monday in solidarity with the prisoners on hunger strike.
In June, authorities released a journalist from the Qatar-based Al Jazeera Arabic channel on medical grounds after he had been on hunger strike for over four months to protest his detention without charges.