By Nuzulack Dausen
DAR ES SALAAM (Reuters) - Nearly 600 refugees left Tanzania to return to their homes in neighbouring Burundi on Thursday, the United Nations said - the first batch in a mass repatriation that some migrants fear could force them back against their will.
Hundreds of thousands of Burundians fled a surge of political violence in 2015 when President Pierre Nkurunziza ran for a third disputed term in office and opponents accused him of breaching the constitution.
A U.N. Commission on Burundi reported last month that there was risk of a fresh wave of atrocities as the landlocked state approached a 2020 election with its political crisis unresolved.
But Burundi and Tanzania agreed in August to start repatriating 200,000 refugees, saying that conditions in Burundi had improved.
A Tanzanian government official and the United Nations said all of Thursday's returns had been voluntary.
"All refugees who had registered to return home voluntarily from all camps gathered at Nduta camp and departed from there," said Athuman Igwe, responsible for coordinating refugees affairs in Kigoma, western Tanzania.
The U.N. refugee agency, UNHCR, said 590 Burundian refugees had returned on flights that it had organised with the U.N.'s International Organization of Migration (IOM).
It said it had it had not promoted the repatriation programme but was ready to help anyone who wanted to go back.
"We urge the governments of Tanzania and Burundi to respect their commitments to uphold international obligations and ensure that any refugee returns remain voluntary and that no refugee or asylum seeker is returned to Burundi against their will," it added in a statement.
Some refugees have expressed fears that they might be forcibly returned to Burundi after Tanzania's Home Affairs Minister Kangi Lugola said in a video posted to Twitter in August that Tanzania would send home "all Burundians" because "Burundi is peaceful".
(Additional reporting by Katharine Houreld; writing by Clement Uwiringiyimana; editing by Katharine Houreld and Andrew Heavens)