The Arab Organisation for Human Rights (AOHR) said as many as 3,185 civilians have been killed by Egyptian security forces outside the frame of law since 3 July 2013.
The group explained in a report that the victims included 2,194 people who were killed during the Egyptian security forces' attacks on peaceful gatherings, most notably the dispersal of two sit-ins in the Rabaa and Al-Nahda squares on 14 August 2013, and 766 people who had died in detention centres, including 122 people who died as a result of torture, 516 people who died as a result of medical negligence, 37 due to overcrowding and poor conditions in detention and 91 people due to corruption of the detention facilities' administrations.
"In the six years since July 3, 2013, in Egypt, the human rights situation has been continually declining in an unprecedented manner. Security forces have practiced all forms of violations under the climate of complete impunity," the UK-based body said in its report titled "Six Years of Impunity".
The report questioned the causes of death of the late President Mohamed Morsi last month, and whether he was poisoned, criticising authorities for forcing his family to bury him quickly without allowing them to perform the necessary autopsy.
The organisation reported that for six years, the Egyptian regime used arbitrary arrests to suppress opposition.
"According to quantitative monitoring of arbitrary arrests in Egypt, there is an estimated figure of 63,032 people who have been arbitrarily detained since July 3, including 691 women and 1,161 minors," it said.