DAKAR (Reuters) - A hundred unarmed South Sudanese refugees in east Congo took 13 United Nations mission staff hostage on Tuesday, demanding to be moved to a third country before later releasing them unharmed.

They were among 530 people who have been living in the Munigi base, outside Goma, since fleeing South Sudan last August, U.N. Goma bureau head Daniel Ruiz told Reuters.

Most are former fighters loyal to former vice president Riek Machar, who have clashed with President Salva Kiir’s forces since July 2016.

“The camp is quiet and under full control of MONUSCO (the peacekeeping mission),” U.N. peacekeeping spokeswoman Ismini Palla said at the United Nations. “All staff have returned safely to their homes. No casualties have been reported. The mission is investigating the incident.”

The United Nations estimates about 3 million South Sudanese have been uprooted by the violence in their country, the biggest cross-border exodus in Africa since the 1994 Rwandan genocide.

Ruiz said the camp occupants had been demanding for months to be moved to a third country, but no one would take them.

Congo’s government, mindful of threats to its stability from past refugee influxes, and from the armed groups that frequently roam its lawless east, is also keen to move them.

On Friday, eight of them agreed to be repatriated to South Sudan’s capital Juba. Others fear going back and are frustrated at being confined in the tiny camp in eastern Congo.

“They’re saying if the eight were transferred to South Sudan, why shouldn’t we be able to go to a third country?” Ruiz said.

Civil war broke out in oil-producing South Sudan in 2013, after Kiir sacked Machar from the vice presidency.

That conflict ended in a peace pact in 2015 and Machar was reinstated early last year, but tensions between the two men lingered and finally erupted into new fighting in July.