Around 30,000 would-be migrants from sub-Saharan Africa are camped out in Morocco, hoping to enter Spain via its North African exclaves, Ceuta and Melilla. That's according to police sources, who all point to the "enormous migratory pressure" that the two cities are under.

The information comes in the wake of an attempt by hundreds of migrants to enter Ceuta from Morocco on February 6. The incident ended in tragedy, with the death toll from the Tarajal beach crush reaching 15 after two more bodies were found over the weekend. The European Commission has since demanded explanations from Spain as to why officers stationed at the nearby border crossing used rubber bullets to try to deter the group from entering.

Police sources also point to "well-structured criminal organizations," which are dedicated to transporting and channeling the thousands of immigrants who are trying to reach Europe.

However, many of the would-be migrants do not have funds to pay the mafias, meaning that attempting to jump the fences in Ceuta and Melilla is "the only option for them to cross from Morocco to Spanish soil, given that it has no cost and can be attempted at any time," say security sources. Attempting a crossing by boat is riskier and migrants have to pay before embarking.

On many occasions, migrants know the date on which a human stampede against the fence is due to take place in advance. The same sources report that news reached Mauritania that a crossing attempt was to be made on February 6 four days in advance, which prompted one group to immediately begin the trek to Ceuta in order to take part.

The authorities say they are also greatly concerned about the rise in attempts to smuggle immigrants across the border in vehicles with secret compartments.