Spain's prime minister has defended the way Moroccan and Spanish police repelled migrants last week as they tried to cross the shared border into the North African enclave of Melilla.

He depicted the attempt in which at least 23 people died as "an attack on Spain's borders".

"We must remember that many of these migrants attacked Spain's borders with axes and hooks," said Prime Minister Pedro Sanchez during an interview with The Associated Press.

"We are talking about an attempt to assault the fence that was evidently carried out in an aggressive way, and therefore what Spain's state security forces and Moroccan guards did was defend Spain's borders."

Authorities in Morocco have blamed the deaths on a "stampede" of people that formed on Friday as hundreds attempted to scale or break through the 12-metre iron double fence.

The barrier surrounds Melilla, a town of 85,000 separated from the Spanish mainland by the Strait of Gibraltar.

Non-profit groups working in northern Africa and human rights organisations have deplored the treatment the migrants received from police on both sides. But they have also directed their blame at Spanish and European Union officials who they say have essentially outsourced border controls to Morocco and other states.

Mr Sanchez, whose left-to-centre government is trying to improve ties with Morocco following an acrimonious diplomatic dispute over Western Sahara, has refused to criticise the crackdown.

Speaking at the palace on the outskirts of Madrid that hosts his office and residence, Mr Sanchez told AP that his thoughts were with the families of those who died.

But he blamed the tragedy on "international human trafficking rings who are profiting from the suffering of human beings who only want to seek a better life".

"I insist, these are international mafia groups that are not only damaging the territorial integrity of Spain but also that of Morocco, which is a country suffering that irregular migration," he added.

Mr Sanchez spoke to AP on the eve of hosting Nato leaders in a summit that aims to redraw the defence alliance's strategy for the next decade.

While Russia's invasion of Ukraine will take centre-stage at the two-day meeting, the group will also debate its posture on Africa, where Russian mercenaries are adding to concerns about migration, extremism and the impacts of poverty and climate change.

Footage uploaded to social media shows how a large number of migrants approached a section of the fence and began scaling it. Some of the migrants hurled rocks at Moroccan anti-riot police trying to stop them. At one point, the fence collapses, sending many of the migrants to the ground from a height of several metres.

In at least one video released by a Spanish online news website, Spanish guards can also be seen escorting migrants back to the Moroccan side, a practice that human rights activists say denies the right of refugees to apply for asylum on European soil.

At least 76 civilians and 140 security officers on the Moroccan side, and 60 National Police and Civil Guard officers on the Spanish side, were injured, according to their respective governments. A small group of African men who did make it across the fence were taken to a migrant holding centre in Melilla.

While Moroccan authorities say 23 people died in addition to scores of injuries both among the migrants and border guards, activists claim that the death toll is higher and denounce the EU's policy of striking deals with Morocco and other states such as Turkey to control migration flows.

A group of 51 human rights groups said on Monday in a joint statement distributed by Spanish NGO Walking Borders that the deaths "are the tragic example of the European Union's policies of externalising its borders, with the complicity of a southern country, Morocco".

"The death of these young Africans at the borders of 'Fortress Europe' is a warning of the deadly nature of the security co-operation on immigration between Morocco and Spain," the statement added.