African Union Commission (AUC) Chairperson Moussa Faki Mahamat called late Sunday for an "immediate investigation" after the deaths of dozens migrants trying to cross from Morocco into the Spanish exclave of 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, with the ensuing violence leading to the deaths of at least 23 people and injuries to many more," Mahamat said on Twitter.

"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 prioritize their safety and human rights, while refraining from the use of excessive force," he added.

Around 2,000 migrants, many from Sudan, tried to cross the militarized border fence Friday and were met with force from both Moroccan and Spanish authorities.

Initial reports indicated five dead, but Moroccan authorities later raised that figure to 23. Helena Maleno Garzon, head of the NGO Walking Borders, said at least 37 people lost their lives.

Earlier on Sunday, the Moroccan Association for Human Rights (AMDH) published an image showing authorities from the North African country digging around 20 graves, which the organization says were meant for the migrants who died in the pandemonium.

On Saturday, several non-governmental organizations released a joint statement demanding a probe into the treatment of migrants during their attempt to cross the border. The AMDH specifically pleaded against burying the bodies without an investigation.

Meanwhile, Spanish Prime Minister Pedro Sanchez has only applauded Spanish and Moroccan collaboration on the border, saying the mass migration attempt was "well resolved."