Egyptian police arrested 516 supporters of the blacklisted Muslim Brotherhood during violence that erupted as the country marked the fourth anniversary of its January 25 uprising, the interior minister said Monday. "Yesterday, we arrested 516 elements from the Muslim Brotherhood group who were involved in firing ammunition, planting explosives and bombing some facilities," Interior Minister Mohamed Ibrahim told a press conference in Cairo. The authorities have engaged in a bloody crackdown targeting the Muslim Brotherhood since former army chief and now President Abdel Fattah al-Sisi ousted his Islamist predecessor, Mohamed Morsi, in July 2013. Rights groups such as Human Rights Watch have repeatedly accused the security forces of unleashing "excessive force" while dispersing demonstrations backing Morsi, who belongs to the Brotherhood. Ibrahim said 20 people were killed Sunday in clashes that erupted between security forces and Islamist protesters. He said most of the victims were in Cairo's northern district of Matareya where clashes lasted for more than 12 hours, adding that those killed included two policemen.