The United Nations' refugee agency says it has airlifted 132 vulnerable migrants from Libya to Niger, the first group to be flown out after a two-month halt in such evacuations.

The U.N. High Commissioner for Refugees says the group of refugees and asylum-seekers was flown from Tripoli to Niger's capital, Niamey, on Thursday. UNHCR's humanitarian evacuation program had been halted in early March amid concerns from Niger's government that migrants were arriving there faster than previous arrivals could be resettled elsewhere.

UNHCR tried to fly out the migrants on Tuesday but the flight had to turn back to Tripoli because of technical problems.

The U.N. has been trying to empty government-controlled detention centers in Libya as part of a stepped-up effort to tackle the smuggling and slavery of migrants.