Nearly 600 African migrants in Algeria were abandoned in the desert with hardly any food and water before being rescued, an official in neighbouring Niger said on Sunday.
Rights groups have accused the Algerian authorities of arbitrarily arresting and deporting migrants from sub-Saharan Africa and sometimes dumping them in the desert, charges vehemently denied by government.
"Three days ago a first wave of 180 Nigeriens arrived in Agadez followed by another wave of at least 400 foreigners," a senior municipal official in the northern Niger city said.
Agadez, known as the gateway to the Sahara, has become a key hub for African migrants trying to reach Europe.
The official, who spoke on condition of anonymity, said the migrants, including children and many women, had been "abandoned" in "the usual atrocious conditions near the border with Niger".
"According to the migrants, they were taken close to the border and dumped," he said.
"Left with a minimum of food and water (they) walked a good 50 kilometres (30 miles) before being rescued."
Some of the migrants were now sick, he said, adding that all were being looked after by local and other West African authorities and the International Organization for Migration.
IOM Niger representative Giuseppe Loprete said in a tweet his agency had assisted 391 migrants of 16 nationalities including Ivorians, Senegalese, Guineans and Cameroonians "abandoned on the border with Niger and Algeria".
But Algeria lashed out at the UN body.
"What the IOM is not saying is that it does not do anything to help them (when they are in Algeria). It is Algeria that provides them with assistance by distributing food kits and water," interior ministry official Hassen Kacimi said.
He said Algeria has suggested that the IOM set up a system in Assamaka, a Nigerien town about 15 kilometres from the border, to rescue migrants prevented from returning to Algeria, but "the IOM is completely absent on this".
Algerian Interior Minister Noureddine Bedoui also denounced "a campaign of non-constructive and unfounded criticism" against his government.
"(Algeria) has always supported African migrants and spared no effort, including humanitarian, to lend them aid and assistance," he said at a Algeria-Niger meeting on border security cooperation.
Since the beginning of the year, the IOM said it has conducted 18 rescue operations in the area involving 3,000 people.
The IOM has reported a sharp rise in the number of migrants left to walk across the border between Algeria and Niger through the desert, up from 135 in May 2017 to 2,888 in April this year.