Melilla is the Spanish enclave in Morocco, and one of only two land borders between Africa and Europe.
At least 37 African migrants have been killed and 100 injured after Moroccan border police tear-gassed and hit migrants attempting to cross into Spain.
The incident took place at the border between Nador and Melilla last Friday.
Melilla is the Spanish enclave in Morocco, and one of only two land borders between Africa and Europe.
In a report by Reuters, about 2,000 migrants took part in the attempt, triggering violent skirmishes with Moroccan security forces and Spanish border guards at the Melilla enclave, with about 100 managing to get across.
Spanish Prime Minister Pedro Sánchez described the events as a "violent and organised act by mafias that traffic human beings to a city that is in Spanish territory. It was an attack on the territorial identity of a country in a violent manner."
However, several human rights bodies have condemned the activities of the police forces, following images from the attack disseminated on social networks and in the media which showed the forceful attacks on migrants.
The organisations have called for the immediate launching of an independent judicial investigation by both Morocco and Spain, as well as at the international level, to shed light on the tragedy.
An independent investigation must include representatives of the migrants, trade unions, and NGOs.