Five migrants died when hundreds of Africans stormed razor wire fences between Morocco and a Spanish enclave on Thursday. Spanish news reports said they had been shot.
Two bodies were found in Spain's North African outpost of Ceuta and three bodies in Moroccan territory after a night-time assault by up to 600 Africans on two fences surrounding the territory. Up to 50 migrants were injured.
Growing controversy over how the migrants died embarrassed Spanish Prime Minister Jose Luis Rodriguez Zapatero and Moroccan counterpart Driss Jettou as they discussed illegal immigration at a summit in the southern Spanish city of Seville on Thursday.
Zapatero declined to comment on reports the migrants had been shot, but promised a rigorous investigation. Spain and Morocco had agreed to give accurate, joint information on their findings, he told a news conference in Seville.
The tragedy also put pressure on both sides to sort out chaos on Europe's only land borders with Africa.
Spain announced it would beef up security at Ceuta and its other North African enclave Melilla by sending 480 troops while Jettou said Morocco had recently deployed 1,600 extra security force members along the coast, reports Reuters.
According to BBC, at least 28 would-be immigrants were being treated in hospital for injuries, the regional government said.
Morocco and Spain are geographically so close that Africans pour into Morocco from all over the continent in an attempt to enter the European Union.
EU justice and home affairs commissioner Franco Frattini said on Thursday: "This tragedy, once again, bears witness to the urgent need for a genuine and effective management of migration issues."
Spain has recently raised the height of fences in Ceuta and Melilla and posted more soldiers there, while Morocco is putting a tighter watch on its coastline.
Over the last few weeks would-be immigrants have been using ladders and what Spanish officials have described as "military tactics" in their increasingly desperate attempts to get over border barriers.