NIAMEY (Reuters) - Algeria has deported nearly 400 African migrants trying to reach Europe, sending them back over the Sahara desert into neighboring Niger, the U.N. migration agency (IOM) and Niger said on Sunday.

The IOM and European Union are intensifying efforts to return African migrants home, after thousands have died making the dangerous crossing to Europe across the Mediterranean in overcrowded boats. Many get stuck before ever reaching Africa’s northern coast, either in Libya, where they suffer slavery and abuse at the hands of militias, or Algeria.

IOM operations officer Livia Manente told Reuters in an email that the group of 391 migrants from 16 west and central African countries had arrived in the Nigerien town of Assamaka on Friday on about 20-30 vehicles, after being stopped while heading to work in various Algerian cities.

“They claim their phones were confiscated and that conditions were poor -- not much food and water, crowded rooms),” she said. “They were transported in trucks after the locality of In Guezzam and then obliged to walk across the border ... including families with pregnant women and children.”

Aboubacar Ajouel, the mayor of Agadez, the last destination for the migrants, confirmed that they had arrived.

Algeria declined to confirm this particular deportation, but said that 20,000 migrants had been prevented from reaching Europe by Algerian authorities since January, thanks to security measures put in place at its borders with Mali and Niger.

“We have no choice but to prevent them,” Hassen Kacimi, director of Algeria’s interior ministry in charge of migration, told Reuters by telephone.