Amnesty International Monday denounced the "utter carnage" in Egypt, after clashes between security forces and supporters of ousted president Mohamed Morsi killed hundreds across the country in the past week.
The London-based rights group also said the international community's response to the political crisis in Egypt, where the clashes between Islamist protesters and security forces left more than 800 people dead since August 14, was "weak and ineffective".
"A clear violation of international law and standards has been carried out in Egypt in what can be described as no less than utter carnage," Salil Shetty, Secretary General of Amnesty, said in a statement issued on Monday.
Amnesty urged the interim authorities to "take immediate action to prevent further loss of life, while bringing security and public order back to the streets".
"The interim government has already stained its human rights record -- first by breaking its promises to use non-lethal weapons to disperse pro-Morsi sit-ins and allow for the safe exit of wounded and then by justifying their actions despite the tragic loss of lives," Shetty added.
He also criticised the international community sharply over their reaction to the Egypt bloodshed.
"The response of the international community has been weak and ineffective, even as everyone leaps to condemn the horrific loss of life," he said, urging it to "act decisively to send a message that no government can behave this way and retain any credibility."
Shetty said that even if some of Morsi's supporters had used violence against the security forces as they broke up demonstrations calling for the Islamist president's return, "that could never justify such a disproportionate response" from police and troops.
The head of Amnesty International in Germany, Selman Caliskan, said that only a "comprehensive investigation can ensure justice for the victims and accountability for the perpetrators".
Amnesty has criticised the security forces' response to pro-Morsi protests several times since the army toppled and arrested him on 3 July after popular mass protests against his presidency.