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.

Algeria has often sent migrants back to Niger since 2014 as the number of people taking the dangerous route to Europe from West Africa has swelled. But the latest group is different because it involves people from across the region, not just Niger, officials said, suggesting a more determined effort to remove immigrants.

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.

"They are about 1,000, 271 from Niger, the rest from West African countries, mainly Mali and Guinea Conakry," said Giuseppe Loprete, the head of IOM's mission in Niger.

Algerian and Nigerien authorities were not immediately available for comment.

The IOM, which has a holding center in Agadez where migrants from across the region are housed and fed, is not directly involved in the latest deportation, as it was not contacted by Algerian or Nigerien authorities to help, Loprete said.

The migrants are instead being housed on the outskirts of town, said Isatou Abdou, who works for the U.N.'s human rights arm in Agadez. She could not immediately confirm the numbers.

According to a Human Rights Watch report released on Friday, over 1,400 migrants have been forcibly deported from Algeria this month. Many were rounded up in the capital Algiers and bused to Agadez, over 1,600 miles (2,600 km) south.

"A mass and summary deportation of migrants, including men and women who may have fled persecution or have worked for years in Algeria, would violate their rights," said Sarah Leah Whitson, Middle East and North Africa director at Human Rights Watch.