Egypt's general prosecution ordered on Saturday the detention of journalist Mahmoud El-Sakka for 15 days pending investigation on charges of allegedly publishing "inaccurate and false news."
The prosecution did not, however, divulge what news the journalist allegedly falsely reported.
El-Sakka works for the left-wing website Bawabet Yanayer, which was founded in 2014 by activist Amr Badr and a group of progressive journalists and supporters of the 25 January 2011 revolution.
He was reportedly picked up by security forces in the Cairo district of Mohandessin on Thursday.
His whereabouts remained unknown to family and friends for more than 24 hours prompting the Journalists Syndicate to file a report to the prosecutor general demanding answers.
The syndicate has also cited in its complaint a number of constitutional provisions and international conventions, including Article 41 of the Egyptian Constitution that states that "Personal freedom is a natural right that is safeguarded and cannot be infringed upon. Except in cases of in flagrante delicto, citizens may only be apprehended, searched, arrested, or have their freedoms restricted by a causal judicial warrant necessitated by an investigation."
The complaint also listed other international conventions that restrict the detention of journalists.
According to the syndicate, in 2015 around 23 Egyptian journalists have been imprisoned while in 2014 around 12 were in jail.
A number of political activists have been arrested in the past few days in what is believed to be pre-emptive measures against "rumoured" protests ahead of the fifth anniversary of the 25 January Revolution.