Over the past 10 months, more than 15,000 from Niger and 1,300 from other countries have reached the two transit centers -- one in Arlit, closer to Algeria, and the other in Dirkou, nearer to the Libyan border.
Some who've made their way back from Libya have told of being held in detention where they suffered harsh treatment, Lungarotti said.
Before Libya's revolution overthrew the regime of strongman Moammar Gadhafi two years ago, many migrants from Niger worked in its construction and agricultural sectors. But the instability forced many out.
The recent conflict in northern Mali also sent about 60,000 refugees over the border into Niger, according to the European Community Humanitarian Office, adding to the pressure on its meager resources.