Human Rights Watch (HRW) is calling on Egyptian security forces to stop using live ammunition against demonstrators as pressure grows on the army to stop its deadly crackdown on protesters.
In a report released on Monday, HRW accused Egyptian security forces of using excessive force when they moved to clear the larger of the two protest camps in Cairo on August 14.
The New York-based group said the assault amounted to the "most serious incident of mass unlawful killings in modern Egyptian history."
It called on authorities to reverse a recent decision authorizing the use of deadly force by security forces when they come under attack or when key government facilities are assaulted.
"This excessive and unjustified use of lethal force is the worst possible response to the very tense situation in Egypt today," said Joe Stork, the deputy director for Middle East and North Africa at Human Rights Watch.
"Egypt's military rulers should rein in police forces to prevent the country from spiraling into further violence. The military should not be encouraging police to use even more lethal force," he urged.
Meanwhile, an Egyptian rights group has called for an independent inquiry into the death of hundreds of protesters in the security crackdown that started last week.
Egypt has been experiencing unrelenting violence since July 3, when the army toppled Mohamed Morsi, the first democratically elected Egyptian head of state, suspended the constitution and dissolved the parliament.
Almost 900 people, including nearly 100 soldiers and police, have died in clashes across Egypt since August 14, when the interim Egyptian government launched a brutal crackdown on thousands of peaceful protesters demanding the reinstatement of deposed president.
Amnesty International has called for a thorough and unbiased probe into the last week massacre of Morsi supporters in the capital.
On Monday, United Nations Secretary General Ban Ki-moon said he was "deeply disturbed" by the death of 37 Muslim Brotherhood detainees on the way to a north Cairo jail, and called for a "full investigation to ascertain the facts surrounding this incident."