Human Rights Watch is urging the United Nations to investigate several incidents of mass killings by Egyptian security forces loyal to then-President Mohamed Morsi last year, the watchdog group said Tuesday. The appeal comes after a yearlong investigation found evidence that Egyptian police and army committed crimes against humanity when they opened fire on demonstrators in Cairo during the 2013 protests to oust Morsi, Human Rights Watch revealed in a new report.

“In Rab'a Square, Egyptian security forces carried out one of the world’s largest killings of demonstrators in a single day in recent history,” Kenneth Roth, executive director of Human Rights Watch, said in a statement. “This wasn’t merely a case of excessive force or poor training. It was a violent crackdown planned at the highest levels of the Egyptian government. Many of the same officials are still in power in Egypt, and have a lot to answer for.”

The New York-based human rights group documented 817 people killed in one clash with protesters alone. The report recommends that top-ranking Egyptian security force officials be held accountable for these and other killings. The report documents several times where unarmed demonstrators were killed by snipers shooting from nearby buildings or even from helicopters.  

“It is appalling and heartbreaking that the hopes of so many Egyptians following the 2011 uprisings faded into the bloodshed and carnage of last year’s mass killings,” Roth said.

Morsi was overthrown by the military on July 3, 2013, following several days of demonstrations.