International rights groups are criticizing the Egyptian government for failing to hold officials accountable two years after one of the deadliest dispersals of protesters in the country's history.

Hundreds were killed in a single day when Egyptian troops moved in to disperse sit-ins by Islamist supporters of the Muslim Brotherhood on Aug. 14, 2013.

Friday marks the second anniversary of that crackdown, which came a month after the military's ouster of Islamist President Mohammed Morsi, following mass protests against him.

To mark the anniversary, hackers attacked the website of Cairo's International Airport, posting a message promising to pursue the culprits behind the deadly dispersal.

The New York-based Human Rights Watch called for a U.N. inquiry into the dispersal. The Paris-based International Federation for Human Rights urged an independent investigation.