It has also begun deporting thousands of sub-Saharan Africans who are living in Algeria without consent — typically from countries such as Mali, Cameroon and Nigeria.

The result is a southward stream of migrants across the sparsely populated region in temperatures of up to 120 degrees.

On a single day last month, 1,500 arrived at the remote border village of Assamakka, according to Giuseppe Loprete, IOM chief of mission in Niger.

Migrants dropped there by Algerian authorities face a 250-mile journey to the nearest town, Agadez. Many give up seeking transport and walk.

Check this: #migrants crossing the border from #Algeria to #Niger walking at 45 C after having been abandoned or sent back. Migrants from #Mali #Cameroon #Guinea and all #ECOWAS join their voices: « we are treated like animals ». Long way home but now safely with @OIM_Niger. pic.twitter.com/CxydftuUyt — Giuseppe Loprete (@g_loprete) May 2, 2018

“Most of them have no money or identity documents, food or water,” Loprete said. “They are traumatized. In some cases they have been unable to get transport and have walked or they have been abandoned by human traffickers and don’t know where they are."

At least 7,000 are expected to pass through in the year to June, according to IOM estimates, often carrying children or a few belongings.

In the desert heat, one day without water is enough to cause death from dehydration.

The Algeria-Niger border, in red, is a busy route for migrants. Google Maps

“The territory makes it difficult to verify numbers but most groups we find have reported deaths along the way,” Loprete said. “Recently we found a group that started out as 50 but only six remained alive. The total number of deaths must be in the dozens in this current crisis and definitely in the thousands since 2015.”

Niger's border with Libya is formally closed and heavily militarized, and so the Algeria border has become a major destination.

No official figure is available for the number of undocumented migrants in Algeria, but some unofficial estimates put the total as high as 100,000.

A hangar at the Algeria-Niger border where migrants escape from the sun. @IOM_NIGER_2018

Algerian Foreign Minister Abdelkader Messahel last year said migrants are “a threat to national security” and vowed to step up deportations.

Despite the uptick in deportations and the risk of death on route, there are still some migrants heading north in search of a better life.

It means the IOM camps in Niger are dealing with flows of people in many directions.

#migrants from #algeria now with @OIM_Niger:« we have papers, black men suffer there, 2 died on the route nobody did anything ». Is their voice heard? - « On a les papiers, les noirs on souffre là bas, 2 sont morts sur la route personne a rien fait ».Leur voix est-elle entendue? pic.twitter.com/E4yVtj1UmM — Giuseppe Loprete (@g_loprete) May 7, 2018

“We can only explain the dangers and give them advice,” IOM's Loprete said. “Some are determined to go into Algeria but a lot of them get robbed by the traffickers and end up back here with no money. Some just give up and go home; we can arrange that with consular help."

Human Rights Watch has reported that Algerian officials are rounding up migrants from streets or construction sites and holding them in crowded deportation centers before expelling them over the border into Niger.