The Free Front for Peaceful Change movement has accused the Muslim Brotherhood of abducting and torturing Ibrahim Hanafi, one of its leading members in the eastern Delta governorate of Sharqiya.
According to a statement issued by the front on Friday, Hanafi was forcibly disappeared by "Muslim Brotherhood militias" for a few days in Sharqiya.
"The Muslim Brotherhood abducted and tortured Ibrahim Hanafi, dumped him completely naked and beaten in a desert area on the outskirts of the 10th of Ramadan city east of Cairo, and left a written note next to the victim threatening the members of front they would meet the same fate as Hanafi," the statement said.
The front said Hanafi filed a police report about the incident with the 10th of Ramadan police accusing the Muslim Brotherhood "of terrorising him in order to force him to stop his anti-Brotherhood activism."
Hanafi claimed in the complaint that unknown individuals forced him into a microbus, blindfolded him before leading him to an unmarked destination where they beat him and poured hot water on his body for a period of time.
However, Ahmed Gaber El-Hag, the media coordinator for the Muslim Brotherhood's Freedom and Justice Party, described Hanafi's accusations as completely false and baseless.
"The use of violence is not our style," El-Hag said explaining that in recent weeks the Brotherhood's opponents have maliciously accused the organization of crimes it not commit in order to systematically tarnish its image.
Hanafi went missing four days ago after he attended a protest against President Mohamed Morsi at the Itihadiya presidential palace in Heliopolis, Cairo.
On Thursday night, policemen found Hanafi naked with his hands tied behind his back during a regular patrol.
Hanafi's case comes on the heel of a series of incidents of abduction and murder of several revolutionary activists in recent weeks.
In a highly publicised case, friends and families of Mohamed El-Gendy, a revolutionary activist from Tanta in the central Delta, have charged that Central Security Forces abducted, tortured and killed the 28-year-old in late January.
A coroner's report issued on Wednesday, however, said El-Gendy died as a result of a car accident.
Meanwhile, more than a dozen women protesters have faced sexual assault including rape at the hands of unknown assailants in the last two weeks around Tahrir Square.