Spanish authorities in the enclave of Melilla in North Africa are reinforcing border fences targeted by immigrants trying to leave Morocco.
Immigrants have used home-made ladders to scale the fences (Image: Melilla Hoy)
On Tuesday, 12 were injured when a group of around 70 tried to cross the double fences using home-made ladders. Three have died since August.
Spain's Guardia Civil says it is working to bring all the fences up to six metres in height.
Some rights campaigners have criticised the force used against the immigrants.
Melilla and Spain's other African enclave Ceuta are targeted by immigrants, many from sub-Saharan Africa, as stepping-stones to the European Union. Many migrants are caught and many drown while attempting to make the sea crossing to Spain.
A Guardia Civil spokesman said groups had been trying to cross at the lower points in the perimeter fencing. It is at these points where work is being carried out to raise the height.
"But I think they will still try to cross," he said.
Two immigrants died after an attempt by around 300 immigrants to storm the border fences on 27 August. A third died in another bid two weeks' later.
Those injured in Tuesday's attempt are said to have hurt themselves falling from the fences.
Spanish guards on the borders have responded to the attempted invasions with anti-riot methods.
The Doctors Without Borders (MSF) charity criticised what it called "the violence" used by the Spanish and Moroccan security forces.
Carlos Ugarte, of MSF, asked what reaction people would have if the Guardia Civil used anti-riot weapons against the immigrants who arrive in boats on the Spanish coasts.
On the other hand, "it is seen as normal" to use these tactics against the sub-Saharans who try to cross the Melilla border, he told the Spanish news agency Efe.
Journalist Mustafa Hamed, of Melilla Hoy newspaper said the situation inside Melilla itself was relatively calm. He said he expected immigrants to try and take their chances before the work on the border fences was completed.
Mr Hamed added that the processing centre holding immigrants who had entered Melilla was already at more than double its capacity, with around 800, while it was built for 480.