MELILLA, Spain (AP) – Climbing ladders fashioned from tree branches, hundreds of Africans from the continent’s poorest countries threw themselves over razor-wire fences Thursday to gain a foothold in Europe – the latest human avalanche seeking entry into a pair of barren Spanish enclaves in Morocco.

Five people were killed trying to enter the city of Ceuta, two reportedly shot from the Moroccan side. Spain called out army troops with automatic weapons to patrol the frontier there and in Melilla, another centuries-old Spanish city on the northern coast of the only African country with land bordering a member of the European Union.

Prime Minister Jose Luis Rodriguez Zapatero, speaking after a summit with his Moroccan counterpart Driss Jettou, promised a thorough investigation but avoided pointing fingers.

“It is premature to arrive at conclusions,” Zapatero said.

Spain is used to heartbreaking stories of destitute Africans risking their lives to reach Europe’s southern gateway in hopes of starting a new life.

Dangerously overcrowded boats – often with women who are pregnant or carrying infants – cross the Strait of Gibraltar from Morocco to reach the Spanish mainland. Youths cling to the underside of trucks being ferried across the treacherous waterway. Men pedal across in bicycle-like vessels.

And while midnight dashes up and over the fences outside Melilla and Ceuta are nothing new, the volume of the human waves doing so rose dramatically this summer and particularly this week.

On Tuesday alone, two separate groups of 500 rushed the frontier at Melilla, and Spain says about 300 made it in.

Last year there were seven such attempts, but so far this year the number is up to around 25, including nine since the end of August.

“In the last few days we have had a different phenomenon, an avalanche of immigrants not seen before that surely has circumstantial causes that we will combat,” Zapatero said Thursday.

At least three Africans died in recent crossings, but Thursday’s deaths were the first to include reports of gunfire.

The Spanish government said two Africans died on Spanish soil and three in Morocco. The national news agency Efe quoted sources close to the investigation as saying two of the bodies found on the Spanish side had gunshot wounds from behind, suggesting they had been shot from the Moroccan side.

He spoke as many of the new arrivals in Melilla – virtually all of them young black men, from countries like Nigeria, Mali, Cameroon and elsewhere – lined up for meals under a hot, muggy sun or rested in tents set up to accommodate them at a now-overflowing holding center built years ago.

Eric Aborah, 17, said he left his native Ghana 2½ years ago on an odyssey through a half-dozen countries in Africa before making it to Morocco, where he spent eight months living in the forest before crossing into Melilla on Tuesday.

Felix Akah, a 33-year-old electrician from Cameroon, said he lost his job when the French company he worked for was bought by Americans and he could no longer support his wife and two daughters, aged 1 and 3. He said it took him almost nine months to make his way north to Morocco, hoping to find work in Spain or elsewhere in Europe.

He, Aborah and others described their feat of climbing ladders fashioned from tree branches held together with bicycle inner tubes or strips of fabric and crossing two 10-foot razor wire fences – separated by a thin strip of land – in the middle of the night.

It works like this: prop the ladder against the first fence, climb to the top, try not to fall as a colleague hands you another one, then scamper down and use that second ladder to scale the second fence. Then, just jump.

“It is not easy to climb and you only have to give everything to God and jump,” said Aborah.

Zapatero’s political opponents contend the recent human waves were instigated by Morocco, which claims both Ceuta and Melilla, perhaps to put pressure on the Spanish prime minister at Thursday’s summit.

Aborah, asked if Moroccan authorities urged him to make the crossing, said he did it because he heard a large group of men were going to make their move Tuesday and he simply joined in.

The opposition Popular Party says Zapatero’s Socialist government is in part to blame for the influx, arguing that an amnesty it pushed through Parliament this year for thousands of undocumented foreigners is luring many other Africans in the mistaken belief they too can get papers.

Melilla’s president, Juan Jose Imbroda, who is a member of the Popular Party, said Moroccan authorities are turning a blind eye to the masses trying to get into Spain.

“In Tuesday’s avalanche there were 600 people using 300 ladders,” he said. “When there are 600 people coming, you can see them.”

In a debate in parliament on Wednesday, however, Socialist spokesman Antonio Hernando blamed the wave of arrivals on extreme poverty in Africa.

Many of the immigrants are now in legal limbo. Spain has fast-track deportation agreements with some eastern European and African countries, including Morocco, but not with the poorer ones, which refuse to take back people like those arriving in Melilla. That means Spain cannot expel them and can only hold them in shelters for a maximum of 40 days.

So they are eventually released, usually on the Spanish mainland, but have no work or residency papers and get by on charity or doing menial jobs and getting paid under the table.

Aborah said his goal was simply to reach Spain and that when he crossed over he surrendered to police, knowing they could not deport him and at least he would get food and shelter.

“I know if I come to Spain, my problem is solved,” he said.