A teenage protester has died of the injuries he sustained during an attack by security forces while in police custody in the Egyptian capital, Cairo.

Reports say Hassan Nadi, 15, died in the Bassatin police station in southern Cairo’s Maadi area, after being denied treatment.

The Egyptian teenager was injured after clashes broke out during a demonstration marking the first anniversary of the notorious Rabaa massacre.

On August 14, 2013, after then army chief and current President Abdel Fattah el-Sisi ousted Egypt’s first freely-elected president, Mohamed Morsi, the security forces launched a brutal crackdown on thousands of Morsi supporters at protest camps in Rabaa al-Adawiya and Nahda squares, killing hundreds of civilians.

Human Rights Watch (HRW) said in a report released on Tuesday that the assault was “one of the largest killings of demonstrators in a single day in recent history.”