Algerian authorities have deported hundreds of West African migrants to Niger this week, trucking them thousands of miles across the desert in one of the biggest roundups seen this year, according to officials and human rights groups.

Over the last two days, at least 1,000 migrants came in a convoy of about 50 trucks to Agadez in central Niger, a desert town where migrants from all over West Africa pay smugglers to take them on the treacherous journey north through the Sahara, according to officials in Agadez, the International Organization for Migration (IOM) and Human Rights Watch.