The African Union Commission chief has voiced his shock at the “violent and degrading” treatment of African migrants trying to cross from Morocco into Spain after 23 people died, and called for an investigation in the incident.

About 2,000 migrants stormed the heavily-fortified border between the Moroccan region of Nador and the Spanish enclave of Melilla on Friday. At least 23 migrants died and 140 police officers were wounded in the ensuing violence, according to Moroccan authorities. It was the heaviest toll in years of such attempts to cross the frontier at Melilla.

“I express my deep shock and concern at the violent and degrading treatment of African migrants attempting to cross an international border from Morocco into Spain,” AU Commission chief Moussa Faki Mahamat said in a statement on Twitter late Sunday.

“I call for an immediate investigation into the matter and remind all countries of their obligations under international law to treat all migrants with dignity and to prioritise their safety and human rights, while refraining from the use of excessive force.”